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Gr E S - <^ 7?>V/^? ^^.^

HARVARD UNIVERSITY

LIBRARY

OF THE

Museum of Comparative Zoology

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51 S.W.

MEMOIBS OF THE GEOLOGICAI STJEYEY.

ENGLAND AND WALES.

THE

GEOLOGY OF THE NEIGHBOURHOOD^
OF CAMBRIDGE;

(EXPLANATION OF QUARTER-SHEET 51 S.W.,
WITH PART OF 51 N.W.)

W. H. PENNING, F.G.S.,
A. J. JUKES-BEOWNE, B.A., E.G.S.

WITH A PAL^ONTOLOGICAL APPENDIX,

R. ETHERIDGE, P.R.S., L. & E., Pres.G.S.

FUfiUSHBD BT OBDEB OP THE LOBDS COMM ISSIOITEBS OB HEB MAJ£8TT*S TBBASITBT.

LONDON:

PBINTBD FOB HER MAJESTY'S STATIONERY OFFICE,
AND SOLD BT

Longmans & Co., Paternoster Row ; Tbubneb & Co., Ludgate Hill;

Lbtts & Son, 83, King William Street ; Edwabd Stanfobd, 55, Charing Cross ;

and J. Wtld, 12, Charing Cross :

also bt

Messrs. Johnston, 4, St. Andrew Square^ Edinburgh ;

HoDGBS, FosTEB, & Co., 104, Grafton Street, and A. Thom & Co., Abbey Street,

Dublin.

1881.

Price 4s, 6d,

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NOTICE.

In the ifoUowing Memoir a district is described
-which comprises an area of about 300 square miles.
The information which it contains is so minute in
all details in relation to practical, theoretical, and
Palaeontological Geology, that it cannot fail to be
of use to all persons interested in the Geology of
Cambridgeshire.

ANDREW 0. RAMSAY,

Director-General.
24th May 1881.

N 309. Wt. 6093.

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NOTICE.

The area described in this Memoir was surveyed by Messrs.
PEKNiNa AND Jukes-Browne, under the superintendence of
Mr. Whitaker.

Each of the authors has described the special district which
he surveyed, and the combined results have been arranged in
concert with Mr, Whitaker, who has edited the whole, and
contributed the valuable Bibliographical Appendix, with some
aid from Mr. Dalton.

The Palaeontological Appendix, by Mr. Etheridge, not only
reviews the Palaeontology of the different sub-divisions of the
Chalk described in the Memoir, but also describes a number or
new Cretaceous species.

This Memoir will be a valuable contribution to geological
literature, the university town of Cambridge occupying
the central part of the district ; and it will not be without
some economic value, as the area described includes a great part
of that over which the so-called coproHtes are worked at the
bottom of the Chalk Marl.

Acknowledgments are due to engineers and well-sinkers for
contributions of well-sections and borings.

H. W. BRISTOW,

Geological Survey Office, Senior Director.

28, Jermyn Street, London, S.W.,
1st March 1881.

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CONTENTS.

Page

KoTiOB by the Director General. iii.

Notice by the Director. It.

Chapter I. — ^Introduction. Feculiaritiesof the District. Rivers. Physical

Features. Qeological Formations ..... i

Chapter II. — ^Jurassic Series. Oxford Clay, with List of Fossils. Elme- .

ridge Clay, with List of Fossils - - - • - 5

Chapter III. — Cretaceous Series. Lower Greensand. Gault, with List

of Fossils - - - . - -- -11

Chapter IV — Chalk. General Description and Classification (with Table of
Zones). Lower Chalk, Chalk Marl. Cambridge Greensand (Nature of
the Coprolites. Ori^n of the Nodules. Fossils, Main Outcrop. Out-
liers). Zone of Bhynchonella Martini (Main MasSi Outliers. list of
Fossils) -•--.--- 20

Chapter V.— Lower Chalk (continued). Grey Chalk. Tottemhoe Stone
(Main Mass, Outliers, List of Fossils). Zone of Holaater subglobosus
(Main Mass, Outliers, List of Fossils); - r - - - 43

Chapter YI — Middle Chalk. Melboum Kock, with List of Fossils. Zone
of Rhynchonella Cuvieri (with List of Fossils). Zone of TerebrattUina
gracilis. Lower Division and Upper Division (with List of Fossils).
Chalk Bock (with List of Fossils). Upper Chalk. Zone oi Micraater
cor&ovis (with List of Fossils) - • - - • «>55

Chapter VIL— Glacial Drift (Boulder Clay, Marine Gravels, and Loam) - 78

Chapter VIII. — Post-Glacial Drift. Gravels of the Ancient Eiver

system ..----.--82

Chapter IX.— Post-Glacial Drift. Gravels of the Present River System
(Cam System, Highest Terrace, Intermediate Terrace, Lowest Terrace,
Fauna of the Gravels. Gravels connected with the Wilbraham River
and Fulboum Waters. Valley of the Ouse, Higher Terrace, Lower
Terrace) -.-,---.94

Chapter X. — Recent Deposits (Alluvium and Peat, Warp and Trail) - 112

Chapter XI. — Theoretical Considerations as to the Physical Conditions

under which the Glacial and Post-Glacial Drifts were deposited. 1.

Boulder Clay. 2. Post-glacial Gravels. 3. The Physical History and

Relative Ages of the River Valleys - - *'. -115

Chapter XII. — ^Economics (Coprolites, Agricultme, Water-supply) - r 126

Appendix A. — ^Palaeontology. By R. Etheridge (1. General Account of the
Palseontology of the different Divisions of the Chalk. 2. Description of
new species) -.-...-. 132

Appendix B. — List of Gault Fossils (remanies) found in the " Cambridge

Greensand." By A. J. Jukes-Browne - - . - 149

Appendix C. — Well Sections (Cambridgeshire, Hertfordshire, Huntingdon-
shire) --------- 165

Appendix D. — ^Borings (Cambridgeshire, Huntingdonshire) - - 1<58

Appendix E. — List of Works on the Geology of Cambridgeshire. By W.
Whitaker (1. (Jeological Survey Publications. 2. Chronological List
of Books, Papers, &c.) - - - - - - -170

Index .---.---. 181

K809.

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LIST OF PLATES.

1. FOBBILB. Fig. 1. Scalaria fasciata. Fig. 2. Pinna tegulata. tfig. d.

Inoceramus lotus, var. Beachensis, Fig. 3a. Do. young form, showing
very rugose nmbo.

2. Fossils. Figs. 1, la. Pecten Jissicosta. Figs. 2, 2a-c. Lima echinaia*

Figs. 3, 3a. Avicula filaia* Figs. 4, 4a. Avictda duhia. Fig. 5*
Spondylus aquicostatus. Figs. 6, 6a. Inoceramus convexus^ Fig. 7»
Do. var. quadratua,

3. Fossil^. Figs. 1» la. Pecten fisstcosta^ left valve, showing the divided

or impressed line down the costse. Figs. 2, 2a. lima omaia.
Figs. 8, 4. Anomia papyracea, var. Burwellenais* Figs. 5, 6. Ottrea
aeuiirostris. Figs. 7, 8. Ostrea curvirostris, Ivar. ittflexa^ Figs. 9-11.
Inoceramus proolematicus. Fig, 12* RhynchondlaReedams* Fig. 13.
TerebrattUina yracUiSy var. noduhsa. Fig. 14. TVe&ra^ti/tiia ^roctlM,
var. /ato* Fig. 15. Terebratidina striata, var. triangularis,

4. Map of the Courses of the Ancient and Modem Bivers in Cambridgeshire.

5. Sections illustrating the Conditions of the Water-level in the Chalk

beneath the Grog Magog Hills,
tf. Secdon, from N.W. to S.E., from Somersham, through Cambridge, to

beyond Barrington Hill.
7* Geological Map of the District « • . <- Fbokhsfucb

LIST OF WOODCUTS.

Page

Fig. 1 . Diagram of the Thinning of the Cretaceous Beds along the strike from

S.W,toN.E. 14

,, 2. Diagram of the North-easterly Attenuation of the Gault - - 16

,9 3. Section across the fields about half a mile N.W. of Homiogsey • 33

„ 4« Section in a Coprolite Pit E. of Harlton (Rev. O. Fisher) - - 35
y, 5. Section in a Coprolite Pit between Harlton and Hasliogfield (Rev.

0* Fisher) -------.86

9, 6* Section in a Coprolite Pit N.£. of HasHngfield - - - 37

„ 7. Diagram-Section across the fields N.E. of Haslingfield « - 38

„ 8. Section through Grantchester - - - - - 45

„ S^. Diagram-Section through Beach and Burwell - - - 47

„ 10. Diagram-Section through Victoria Pit, Burwell - - - 51

„ 11. Sketch of Divisional I^nes in Chalk, Cherry Hinton Quarry - - 56

,, 12. Section in Chalk Pit W. of the Obelisk near Harston - - 58

,1 13. Section in Chalk Pit S.S.E. of Litliogton Church - - - 77

„ 14. Diagram showing the slope of the Boulder Clay - - - 84
,1 15, Section in Gravel Pit on S. side of road W. of Whittlesford Bailway

Station ... 4. ... 86

^ 16» 17* Sections in Gravel Pit two miles west of Balsham - - 88

„ 18. Section from Wilbraham Fen to Bottisham - - - - 92

M 19. Section in Gravel Pit half a mile S.E. of Newmarket Bailway Station

I, 20. Section across the Trumpington Gravels - - - - ■ 96

91 21« Section across the Barnwell Gravels ^ - . .^ - 98

^ 22. Section along Drain fiom Fenner's Ground to Hills Boad, Cambridge 102

„ 23. Section across the Cam Valley south of Waterbeach •> - - 103

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THE

GEOLOGY OF THE NEIGHBOURHOOD
OF CAMBRIDGE.

CHAPTER I.— INTRODUCTION.

Peculiarities of the Disteict.

The area of which the geology is described in the following
pages is small, but it is one which possesses pteculiar interest from
the light that its deposits have thrown upon those of more impor-
tance elsewhere. Owing to certain conditions in the physical
geology of the district some deposits, such as the earlier Post-glacial
gravels, have been here exceptionally preserved, in a manner which
elucidates their method of formation. The multitude of sections
in the Lower Chalk have afforded means of dividing that formation
into distinct palaeontological zones, a division which has not, until
recently, been attempted in England.* And the extensive workings
for phosphatic nodules in the so-called *' Cambridge Greensand "
have made clear the relations of that deposit to the Chalk Marl
above, and the denuded Gault below. The extent covered by the
Oxford and Kimeridge Clays is too small for much to be said
upon those deposits, but the few exposures that occur foster the
belief that similar divisions are possible (were the evidence collected
with that view) as have been worked out in the Lower Chalk.

The district is geologically rich from the number of formations
and periods that are represented, as may be seen from a glance at
the map with its many colours, each representing a well-defined
epoch. The Oxford and Kimeridge Clays, with doubtful Lower
Calcareous Grit between them ; the Lower Greensand and Gault,
with an intervening unconformity ; the great erosion which resulted
in the formation of the *' Cambridge Greensand," the Lower,
Middle, and Upper Chalk, with the intermediate definite bands,
may all be seen within a short distance of the town of Cambridge.
And not these only, but examples of the later Glacial Drifts and
the Post-glacial Drifts, so long regarded as presenting the type of
chaotic confusion ; which, now that they are worked out in detail,
fall into a definite sequence; and each division may be studied
within a radius of less than three miles.

The situation of Cambridge in other respects is equally interest-
ing, the town standing just below the confluence of several streams,
up to which point the river was navigable by the war vessels of
early times. The sharp bend of the river and the higher ground
on its left bank marked the site for a ford and station. The town
is on the borders of the low-lying and formerly weird Fenland,

* By Pkof. H^bebt and Dr. Babrois.
N 309. A

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2 GEOLOGY OF THE NEIGHBOURHOOD OP CAMBRIDGE.

but is still under the shadow, as it were, of the higher slopes and
table lands of the great Chalk escarpment.

Rivers.

Our area lies almost entirely within the county of Cambridge,
but it includes also small parts of Essex, Herts, Huntingdonshire,
and Suffolk. It comprises the district which slopes from the
escarpment of the Chalk on the south to the Fenland on the north,
with the intermediate high ground that falls from the western side
towards Cambridge. Hereabouts several streams converge, and
form the River Cam or Granta, which after skirting the town on
its west and north sides passes by Waterbeach to the Fens.

These streams are the Rheey which springs from a bed in the
lower part of the Chalk, and runs east from Wendy, closely following
the base of that formation, until it receives a branch from Foulmire,
when it turns in a north-east direction to its junction with the
Cam, just south of Grantchester.

The Granta rises in the district south of our area,* passes through
the Chalk escarpment by Chesterford to Shelford, where it is joined
by the Bourn or lAuj that also rises in the Chalk, and thence it runs
by Linton to the same 'point of convergence near Grantchester.
Another stream, also called the Bourfiy flows into the Cam at this
point; it rises by a village of the same name, and passes by King-
ston and Toft in a nearly east direction.

The Full Brook runs into the Cam just north of Cambridge ; and
there are in the north-east corner of the district other minor streams
known as " Ditches" or "Loads" which run down to the Fenlands
that border the river for the remainder of its course to the sea.

A short length of the Ouse passes through the area, running
east from St. Ives to the Fens.

Physical Features.

The area treated of in this memoir is comparatively flat and at
a low level, with the exception of the conspicuous Chalk escarp-
ment, one of the Chalk outliers, and the ridge traversed by the
high road running west from Cambridge to St Neots. The first even
rarely exceeds 500 feet, the last is under 200 feet in elevation.
The outlier of Chalk, capped by Boulder Clay, rises from a plain
of Gault on either side, and forms a long narrow ridge, which,
although of no great height, presents an agreeable feature in the
landscape.

The physical conformation of the ground is (with the exception
of the Chalk slope) such as to induce dampness of soil and atmo-
sphere; a characteristic which, as regards Cambridgeshire, has
become proverbial. It is owing not to the rainfall, which in amount
is small, about 23 inches a year, but to the low-lying area being
surrounded by higher ground on all sides but one, by the preponder-
ance of ground sloping to the north, and by the prevalence of clay
soils.

There is another peculiarity in the meteorology of the northern
part of the area at present unexplained, but which deserves investi-
gation. This is the prevalence of certain conditions throughout a
district, of which Chatteris is the centre, that give rise to hail-

* See explanation of Sheet 47.

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PHTSICAL FEATURES. 3

storms, twofold in number and intensity to those which occur else-
where. For insurance purposes the area thus affected is described as
within a radius of 15 miles around Chatteris, and that this is roughly
correct has doubtless been proved by experience ; within the area one
shilling per acre, and without it sixpence per acre, is paid as yearly
premium for insurance against damage by hailstorms. Chatteris
is situate not far from a central point in the southern bay of the
Fens, from which a radius of 10 miles or so would nearly describe
its boundary — ^from Gillsport, by Ely and St Ives, to Peter-
borough — and from which the land rises in every direction, except
towards the fens on the north. It may be that the cul-de-sac thus
formed catches and retains an undue proportion of storms from
the northward, causing them to eddy and discharge within the
area so situated ; certainly the phenomenon is due directly to this
or some other peculiarity in physical conformation.

Another local phenomenon is the " drowning " of the fens, as
the flooding of the tract is locally termed, to which they are
subject from the bursting of banks and sluices. "The Great
Drowned" of 1796, with its many incidents of suffering and ruin,
is painfully reverted to even now by the few survivors old enough
to remember that catastrophe.

Owing to the shrinking and gradual subsidence of the peat and
alluvial deposits which have been laid dry for several years, the
little hillocks or islands of clay protruding through attain a greater
relative elevation. And it is a common notioti with the labourers
on the fens that " the clay rises," indeed it is not easy to convince
them to the contrary.* In one case, for example, on Pidley Fen
there was formerly a ditch to carry off water in a certain direction ;
the spot which 30 years ago was occupied by its lowest end where
the water was discharged, now forms a small hillock of Oxford
Clay some 4 or 5 feet above the surroimding peat.

Geological Formations.

The accompanying taole shows the various formations and beds
that occur in the district, the great gaps between them being marked
by spaces : —

Diyisions shown on the maiv.

Recent - - Alluvium, peat, &c.

{River Gravel connected with the present streams.
River Gravel of an older valley system.
Gravel (? marine) at high levels.

Glacial - - -f ^°^^^®^ Clay.

'1 Gravel and loam in and below the Boulder Clay.

Cretaceous

r Upper.
H3

Chalk ^ Middle.
L Lower.
Gault.
Lower Greensand.

r Kimeridjje Clay.
Jurassic - --{ Lower Calcareous Grit ?
L Oxford Clay,

* See also the Geology of the Fenland, hy S. B. J. Skertchlt, p. 154, Geological
Survey Memoir, 1877.

A 2

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4 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

The Jurassic series is represented in the N.W. corner of tlie
area by the Oxford and Kiraeridge Clays. These formations a.re
of similar lithological character, and very few sections occur where
fossil evidence can be collected, therefore the line of division is very
indefinite.

The brickyard at Box worth (p. 7) is probably, that at Knap-
well (p. 9) is certainly, in Kimeridge Clay ; the line is drawn
below these two points following the form of the ground, and carried
on to the narrow outcrop of calcareous grit which separates the
two formations further W. (in Sheet 52 S.E.)

The grit is probably continuous with a small exposure of cal-
careous rock, a foot or more thick, with Gryphwa dilatata, just W.
of Els worth, a bed not to be confounded with the ^'Elsworth rock."

The Lower Greensand is but poorly represented in Cambridge-
shire, and is, moreover, almost entirely concealed on the western
sides of the area by a widespread sheet of Boulder Clay, a single
small inlying exposure being found in the neighbourhood of Bourn.
It emerges from beneath this covering of Drift near Lolworth, and
thence it may be traced to the north-east as a narrow strip of red-
dish sandy ground between the dark heavy soils of the Jurassic and
Cretaceous clays.

The Gault takes up a far greater area than the Neocomian sands,
but the width of its outcrop varies greatly, and it does not form
such a continuous plain as in the tract to the south-west, where it is
less interrupted by outlying patches of chalk and drift.

The Chalk in its several divisions covers more than half the area
included in Sheet 51, S.W., extending over most of the ground to
the south-east of the long valley formed by the Rivers Rhee and
Cam, 'wdth outliers of considerable size to the westward.

The whole country was at one time covered by Boulder Clay
resting indiscriminately on the older rocks. It now occurs in mass
only on the higher lands, and as outliers at low levels. Upon it
and upon the denuded surface of the underlying beds are gravels
of various ages ; some dating from early Post-Glacial times,
others being undoubted river deposits, but with no relation to
existing watercourses, and, lastly, more recent gravels belonging
to the existing valley systems.

[It may be well to note that the term " Post-i&lacial " is here
used in a local sense, for gravels newer than the Boulder Clay of
the district, and without prejudging questions of classification of
the Drift as a vrhole, or in other parts. — W.W.]

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OXFORD CLAY. 5

CHAPTER IL— JURASSIC SERIES.
Oxford Clay,

This formation occupies all the northern part of the district
down to a line running about E.N.E. from Elsworth, by Boxworth
and Long Stanton to Rampton^ and is not covered to any extent
by Glacial or Recent deposits.

The sections in which it can be examined are not numerous ; but,
"wherever exposed, it is seen to consist of grey or bluish grey clay,
laminated and fossiliferous. Sometimes the clay encloses small
crystals of selenite, and in every case where any considerable thick-
ness is shown, layers of limestone or of septaria occur. These
layers are seldom more than a foot thick, but they are found at
intervals of a few feet only, are fairly persistent over considerable
distances, and indicate the general dip of the formation.

The thickness of the Oxford Clay in this part of England is not
known, but from its dip, outcrop, and similar indications, we esti-
mate it at about 700 feet. A bore-hole was made into the Oxford
Clay at Bluntisham to a depth of 300 feet in the hope of finding
water, and another at Conington to 256 feet, but no springs were
met with, and the work was abandoned.

At Rumbold Farm, which stands on a knoll of Oxford Clay m High North
(Somersham) Fen, there is said to be a hard whitish rock a few feet beneath the
surface, this is probably lower down in the clay than the sandy bed at Fenton.
At a higher horizon are the bands of limestone and septaria exposed in the
cuttings on the St. Ives and March Railway, and on the new line from St/Ives
to Sutton through Bluntisham and Earith. On the eastern slope of the cut-
ting, a short distance south of Somersham station, three bands of septaria or of
hard sandy limestone may be traced, although partly obscured by slips and
overgrowth. The lines are about 6 feet apart, and appear nearly horizontal.
About 6 feet above the highest bed there occurs a thin, but apparently very
persistent, layer of hard, ferruginous purple-coloured clay, fossiliferous, and
presenting some markings of a very peculiar character.

There are two large pits at Fenton, one mile N. W. of Pidley, one on each
side of the road, from which the clay is dug for brickmaking ; that on the
west side shows 16 feet of bluish-grey clay, with crystals of selenite. The pit
on the east side of the road, at a lower level than the other, 8 feet of grey clay,
with a hard sandy bed 6 inches thick (in places only) in two or three layers.

The large cutting midway between St. Ives and Somersham is mainly through
Boulder Clay, by which the ridge of high ground between those two places is
capped, but in its lower part the Oxford Clay is exposed. Half a mile to the
west of this cutting is a small spring, shown on the map as " The Spa," its
water is slightly cMybeate, and is thrown out probably by a hard bed in the
clay, which is not, however, seen in any section.

The long cutting, just S. W. of Bluntisham on the new line is almost entirely
in Oxford Clay, which here encloses inimmerable minute crystals of selenite.
At its eastern end there is a bed of hard sandy limestone a foot thick, at about
the level of the railway. At one point this bed is faulted, or rather bent down,
for about two feet, the fractured ends of the stone are separated by a gap of
2 or 3 feet, but they incline towards each other and evidently have been con-
tinuous. A large lump of oyster rock projects from the slope of the cutting
on the southern side, but it is not clear whether this is part of a bed in place,
or a boulder from the Boulder Clay, which comes on a little nearer to the
station.

The western end of the same cutting exposes two bands of rock in the clay,
about 2 feet apart ; the lower is rather more than 1 foot thick, hard, sandy, and
calcareous ; the upper is thinner, less hard, and less persistent. These bands
are a little above the rail level, but whether either be continuous with the band

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6 GEOLOGY OF THE NEIGHBOIJBHOOD OF CAMBBIDGE.

at the eastern end of the cutting was not apparent, several chains of the hill
remaining to be cut through when these observations were taken (L877). The
intervening portion, however, gave an opportunity of taking the dip of these
beds, which was found to vaiy from 2° to 3° in a direction nearly north, that
is, into the hill, as might be expected. This shows that the Oxford Clay, after
rising to the north from beneath the Kimeridge Clay and the Neocomian
beds, again sinks slightly in the same direction. The vidley of the Ouse forms
no exception to the general rule, but (hereabouts at least) has been cut deepest
along an old anticlinal ; and by the inward dip, above mentioned, the present
ridge to the north has beenjpreserved from denudation.

Another cutting on the new line, about three-quarters of a mile from the
junction, shows two similar bands at about the same level, doubtless extensions
of the same beds. There is a pit a few feet in depth close by the junction, but
only clay is exposed.

The brickyard, half a mile north of St. Ives, is in fossiliferous blue clay ; that
half a mile further east is in the same clay, but exposes in places only (the section
is overgrown and indefinite) a yellow hard band a few inches in thickness.

The large brickyard just west of St. Ives, near the edge of the alluvium,
gives several small but good sections ; the old high face on the north side of
the pits, and in which all the beds might have been seen at one glance, being
now overgrown. These sections occur in different parts of the fieM, the thick-
ness of the clay between the harder beds exposed cannot, therefore, be easily
estimated, but the general succession is as follows : —

1* Grey clay.

2, Fine purple calcareous sandstone.

3, Fine yellow „ „

4, Blue clav.

^. Two fairly persistent beds of hard sandy limestone, each about 6 inches
to a foot thick, and with 6 inches to a foot of clay between them.

6, Blue clay,

7. A bed or beds of hard sandy limestone (at the water-level.)

The limestones (5) are probably those referred to by Prof. Bonney, who
says : — '' Two well-marked seams of large flattened concretions, about a foot
" apart, were exposed on the north side of the pit in 1874."* The beds
(2 and 3) of purple and yellow coloured fine calcareous sandstones, may rejjre-
sent the Lower Calcareous Grit, which occurs between the Oxford and Kim-
eridge Clays at Papworth St. Everard, five or six miles south of St. Ives, or
they may be merely, as Prof. Bonney has suggested, a '^calcareous band which
" we may call, for distinction, the St. Ives Rock.*'t We are, however,
inclined to think that as the Oxford Clay rises into a slight anticlinal beneath
the Ouse valley, this patch is at too low a level to represent the Calcareous
Grit, and that it is much more likely to be on the horizon of the Elsworth
Rock.

A much thicker rock than any of those already mentioned has
been found at Elsworth, and described by Prof. Seeley as the
" Elsworth Rock."t ^^A dark blue homogeneous limestone ; ... its
thickness is very variable, «... commonly about three or four
feet, though in some places not less than seven feet. On the top
of it is a clay, of a reddish-brown, about five feet in thickness,
and then an upper rock of 18 inches." This band of limestone
is not shown in an)r existing section, except slight exposures by
the brook-side, but its outcrop may be approximately traced, and
is represented by a dotted line on the map (Sheet 51 S.W.)

The brickyard north of Boxworth ia in bluish-grey clay (which may be

* Cambridgeshire Geology, p. 10 {note).

t Ibid. p. 11.

X Ann, Nat. Hist. Ser. Hi., vol. x., p. 98, (1862.) By some mistake Prof.
Bonnet has stated (Cambridgeshire Geology, p. 14) that this rock has been mapped
by the Geological Survey as Calcareous Grit.

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OXFORD CLAY. 7

either Oxford or Kimeridge), with two thin layers of whitish sandy limestone^
separated by a foot of clay, and very fossiliferous. There is said to be a layer
of septaria, several feet below these limestone bands ; the concretions seen in
the pit contained Ammonites biplex in abundance.

This brickjrard is described by Prof. Seeley, who mentions the occurrence of
a rock here about a foot and a half thick. He says, '' the workmen call it
* flint/ a name I have also found given in the surrounding district to the
septariouB concretions of the clays. It is dark blue, very hard, and divided
into layers much as is the Elsworth Rock. The only specimen of it I saw was
a slab from the upper part, about six inches in thickness, which consisted of two
layers, an upper dark blue one with a few small shells scattered about in it,
and a lower pale brown layer composed almost entirely of shells, chiefly uni-
valves." He records the following fossils from this rock; — Ammonites biplex ,
A. aUemans ? Alaria bispinosa, Cerithium muricatum^ Pecten lens.

From the day beneath he obtained Ostrea deltoidea, Grypkaa dilatata, and
another oyster resembling 0. leviuscula. We have also found Exogyra nana ?

The Oxford Clay, of bluish-grey colour, and enclosing small crystals of
selenite, may be seen in a railway-cutting 1 mile N.W. of Long Stanton
Station, in a brickyard north of the cutting, and in an old brick-pit north
of Willingham.

List of Fossils from the Oxford Clay and the included Hocks, com-
piled from the Collections in the Woodwaepian Museum, the
Nomenclature revised by Mr. Etheridgb ; a few Additions have
been made to the Second Column : —

St. Ives
Brickyard,

St. Ives
Rock.

Elsworth
Rock. I

Annuloida :

Acrosalenia spinosa ? Ag.
Cidaris - - - - >

CoUyrites bicordatus, Leske
Pseudodiadema - - - -

Holectypus depressus, Wright
Millericrinus echinatus, Schloth. -
Pentacrinus - - - -

Annulosn - _ _ . -

Glyphcea rostrata, Phil. -

„ scabrosa, Phil, - - -

Serpula tricarinata, Sbg, - - -

„ vertebralis, Sbg.
Vermilia (Serpula), sulcata, Sbg,

Brachiopoda :

Rhynchonella IsBvirostris, McCoy
„ varians, Schloth. -

Terebratula impressa, F. Buch, -
„ insignis, SchUbler

„ intermedia, Sby.

„ obovata (var.), Sby, -

Waldheimia bucculenta, Sby,

JLaniellibranchiata :

Area lEmula, Phil. - - -

„ subtetragona, Morris
„ sp. . - - .

Astarte lucida, Phil,
„ ? ovata, Smith
„ robusta, Lycett -
Avicula in»quivalvis, Sby. (including
A. expansa, Phil.^
„ ovalis, Phil.
„ pterosphena, Seeley

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GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE

St. Ives
Brickyard.

St. Ives
Rock.

Elsworth
Rock.

ZamelUbranckiata'^ cont.

Cardium Sowerbyi, Lycett

...

CacuUaea clathrata, Leck.-

...

• ••

„ (Area) concinna, PhU. -

„ oblonga, Shy, - - -

...

Exogyra nana, Shy.

Gervillia acuta (= lanceolata, Afunst.) -

Goniomya literata, Shy, - - -

...

Gryphfiea dilatata. Shy. -

Hinnites abjectus, Phil. - - -

...

Sedgwicldi

...

Isocardia ^lobosa - _ - .

Lima duplicata. Shy. - - -

...

„ pectinifbrmis, Schloth.

„ rigida (var.), Shy. -

„ sp. - - - -

...

Lithodomus — - . -

...

Lucina Beanii, Lycett - - -

...

Modiola bipartita, Shy. - - -

„ — _ . -
Myacites recurva, Phil. - - -

„ oblata, Shy. . - _

...

Myoconcha crassa, Shy, - - -

Nucula ornata, Quenst. - - -

Opis — ...

...

• a.

Oetrea discoidea, Seeley - - -

„ flabelloides, Lam. - - -

„ gregaria. Shy.

„ ? new sp. -

...

Pecten articulatus, Schloth.

...

„ lens. Shy. - - - -

...

„ vagans, Shy.

...

„ annulatus. Shy. - - -

...

Perna mytiloides, Lam. - . -

...

Pholadomya Phillipsii, Mor.

„ ovalis, Shy. . - -

...

„ tricostata, Seelsy

...

„ aequalis, iSfty.

...

Pinna mitis, Phil. - - - -

,,— ----
Placunopsis, sp. -

..»

Plicatula fistnlosa, Lye. and 3for.

...

Thracia depressa, Shy. - - -

Trigonia clavellata, Lye. - - .

• ■•

„ costata, 5%. - - -

„ elon^ata, Shy. -

Unicardium gibbosum, Lye. and Afor.

...

Gasteropoda :

Alaria bispinosa, Phil. - - -

Amberleya armigera, Lye.

...

..>

Cerithimn Damonis, Lye.

„ muricatum, Shy.

Littoriaa muricata, Shy. - - -

...

Natica clymenia -

...

.*•

Phasinella elegans. Lye. and Mor.

...

Pleurotoraoria reticulata, Shy.

...

Turritella — - -

...

X
X

Cephalopoda :

Ammonites athletus, Phil.

„ BakerlflB, Shy.

...

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OXFOED CliAY.

St. Ives
Brickyard.

St. Ives
Rock.

Blsworth
Rock.

Cephalopoda — cont.

Ammonites biplex, Sbi/. - - -

„ ? canaiiculatus, Sby. -

...

„ cordatus, Sby. (including A.

serratus, 6%., and A. verte-

bralis, Sby,).

„ dentatus, Zieten.

„ Duncani, Sby. (Langton)

„ Eugenii, Rasp.

„ excavatus, Sby. (Over)

„ Goliathus - - -

„ Henrici, 2>'Or6.

...

„ Hecticus, Rom.

Jason, Rein. (St. Neots)

„ Lamberti, Sby.

Marise, 2>'Or6.

„ oculatus, D'Orb.

„ perarmatus, Sby.

„ planicordatus, Sedey -

...

„ Radisensis, 2>'Or6. -

„ Rupellensis, D^Orb, -

„ triplex, Sby. -

Belemnites abbreviatus, MUl.

„ bastatus, Montf.

„ obeliscus (?), Phil. -

„ Oweni, Pra«-

...

Belemnoteuthis - - -

NautiluB bexagonns, Sby.

KiMERiDGE Clay.

The outcrop of this formation occupies but a small portion of
the area, and runs in a narrow belt, partly covered by Drift, from
Knapwell by Boxworth, Oakington, and Cottenham to the fens. It
is a dark blue clay, somewhat shaly, and enclosing near the surface,
in brickyards and other sections, many crystals of selenite. From
the clay in the brickyard north of Knapwell some very clear and fine
crystals have been taken, great numbers of them being 4 inches or
more in length. This is the only exposure of any importance at
present occurring along this outcrop of the Kimeridge Clay, and
shows 15 feet of dark blue clay with fossils, some of which are
filled with iron pyrites. Boulder Clay comes on just above, and a
light-coloured hard calcareous band, full of broken shells, occurs
at the bottom.

Just south of Knapwell the earth thrown out from a freshly cleaned out
pond showed Boulder Clay, with a large heap of dark blue clay (Kimeridge)
beneath. There were many fossils and black phosphatic nodules on this heap,
their profusion indicating a denudation of the clay resulting in the formation
of a " coprolite bed *' previous to the deposition of the Boulder Clay.

Similar phosphatic nodules are found on the surface near where the junction
line of Kimeridge Clay and Lower Greensand crosses the Huntingdon Road
and west of Oakington, showing that a layer of coprolites exists, wholly or in
part, between the two formations ; but it is probably too attenuated to be of
any commercial importance.

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10 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE. ,

The fossils named in the following list were found in the brickyard and
pond above noticed.

Kimeridge Clay Fossils {Knapwell),

Ammonites biplex, Sby,

„ several species.

Belemnites abbreviatus. Miller.

„ species.
Avicuia echinata, Sby,
Exogyra nana, Shy,
Gryphaea dilatata. Shy,
Myadtes ?
Ostrea deltoidea^ Shy,, abundant.

„ gregoria, Sby.
Pecten?

Trigonia clavellata. Young and Bird, cast.
Serpula.
Black phosphatic nodules, in abundance.

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LOWER GBEENSAND. 11

CHAPTER IIL-CRETACEOUS SERIES.

Lower Greensand,

On the western side of the district embraced in our niap the
Lower Greensand is covered by the Boulder Clay (except the small
exposure near Bourn), from beneath which it emerges with a
narrow outcrop east of Boxworth village. It widens somewhat by
the Via Devana, and continues, with a nearly uniform breadth of
about half a mile, by Oakington to Cottenham, where it opens out
over a somewhat wider area ; eastward its surface is overlain by
river gravel for a short distance, but it reappears near the tlough
Inn, on the Ely and Cambridge road, beyond which it passes under
the fen towards Upware and Wicken.

The formation mainly consists of brown and yellow sands, with
some beds of loam ; the sand contains many ironstone concretions,
and is frequently false-bedded. Although there are very few
sections the area occupied by the beds is well-defined by the red-
ness of the soil, which contrasts strongly with that of the Gault
above and of the Kimeridge Clay below.

It might be assumed from the beds making so narrow an outcrop
in a flat district either that the thickness of the formation is but
slight or that the beds dip at a high angle. The actual dip has
not been observed, but it is probable that there is a slight inclination
to the S.E. The narrow outcrop affords no real indication of the
actual thickness of the deposits because they are overlapped by
the Gault, which rests upon them with a slight, and it may be local,
unconformity. The Lower Greensand is thinner tnroughout
Cambridgeshire than along any other part of its outcrop, and its
thickness may be estimated at about 70 feet. A well at Sawston
(see p. 164) gives the thickness as 65 feet. In Bedfordshire the
sands rapidly thicken to 100 and 200 feet, and when they emerge
from the fens in Norfolk their thickness is also much increased.

There are several sections in the small patch exposed by removal of the
Boulder Clay from the valley near Bourn, giving rather high angles of fiise
bedding in difPerent directions.

A sand pit about nine chains west of bend in road at Caxton End showed
five feet of brown and yellow sand, with some coarse layers about three inches
thick, and tabular ironstone concretions with an apparent dip E.N.E. 5°.

In another pit near where the stream crosses the road there is similar sand,
but apparently dipping at about the same angle in a contrary direction.
Traces of Gaidt, witn phosphatic nodules, may be seen in this section between
the Greensand and the Boulder Clay.

In a sand pit at the back of the public-house by the roadside between Bourn
and Caxton End brown and yellow sand was seen to a depth of 12 feet, with
some coarse layers about three inches thick, and tabular ironstone concretions,
with an apparent dip S.W. 28°.

From Lolworth, where the outcrop emerges from beneath the Boulder Clay,
sand and loam may be traced across the fields in a westerly direction to
Oakington, but no open sections were seen. At Westwick its outcrop is much
narrowed by the overlap of the Gault, but the uppermost brown sands are
visible in the deep ditches to the N.E., and nearer Cottenham the outcrop from
beneath the Gault was observed in a deep ditch by the side of the droveway
leading S.S.E. from the road E. of " Cottenham Field." Soft brown sands are
visible at the comer of the roads; these pass up into soft yellowish sandy

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12 GEOLOGY OF THE NEIQHBOUBHOOD OF CAMBRIDGE.

loam, followed by brown clayey loam, which is succeeded by hard mot^dl
Gault without any very marked line of division, though it is probable tha^adbe
Gault is somewhat tinnsprressive over the loam.

The area known as Dunstan Field, south of Cottenham, has a brown sandy
soil, with occasional fragments of ironstone rock scattered over the surface.
The outcrop is again seen in the deep drain just beyond the bridge on the
road from Cottenham to Landbeach, where black clay (Gault) is succeeded by
dark brown ironstone rock, beyond which, to the N.E., come soft brown sands
containing brown phosphatic nodules in some abundance, the whole succession
being very similar to some of the sections at Upware and Wicken.

The Black Clay forms a small outlier on the N.W., where the following
section was seen in the side of a pond : —

ft.
Dry lumpy black clay (? Gault) - - - - li

Hard rock with ironstone lumps - - - - i

Soft brown sand - - - - - - 2

Similar rock and sands are again seen in a pond to the N.E. three-quarters
of a mile west of Goose Farm.

A dark brown sandy loam was exposed in some of the ditches in the fields
half a mile south of this spot ; it appeared to rise up in a low ridge and to
underlie beds of dark grey Gault containing Belemnites minimus and phosphatic
nodules. This loam may be a lenticular bed near the base of the Gault, or it
may indicate a slight unconformity between the Gault and the Lower Green-
sand.

At a small pond just south of the Plough Inn, on the Cambridge and Ely
Road, coarse brown sand enclosing small ft-agments of phosphatic nodules is
visible, and in the ditch leading to Causeway End Farm brown sandy loam
was seen passing into mottled yellow and grey Gault.

Yellow loam may be seen under a thin covering of peat to the north of this
point, which is only 24 miles west of the ouarry at Upware, in the neighbour-
hood of which the Lower Greensand phospnates have been so largely worked.

The ironstone concretions mentioned in the above notes are very general in
the Lower Greensand, and a description of the mode of their formation may
be here reproduced.* Thejr can be seen in every stage in an adjoining area
(Sheet 53 S.E.) in a cutting by Sandy Station, on the Great Northern and
London and North-western Railways, presenting a nearly vertical section 50
or 60 feet in height. The section consists almost entirely of clean sand, in
parts false-bedded, and more or less coloured throughout by the presence of
peroxide of iron. The colour of the sand varies from almost pure white, at
the lower part, through shades of grey and yellow, to a deep rusty brown.
There are here and there layers of hard ferruginous concretions in tabular,
spherical, and many other forms, presenting a feature hitherto (so far as the
writer is aware) unnoticed, in the gradual passage from soft iron-stained sand
to hard complete concretions, exhibiting the various stages in the process of
their formation. This may be best observed toward the northern end of the
cutting, in immediate proximity to and generally beneath the patches of f uUy-
fbrmetl concretions, but it is visible also in other parts of the section.

The first step in the process seems to have been the separation of the per-
oxide into very thin lines resembling stratification, followed by the union of
two or more lines, by attraction or chemical aggregation. These thin layers
of darker colour retain their linear arrangement until about one-eighth part
of an inch in thickness, when the space between them is reduced to about 3 or
4 inches, and they follow the lines of true or false-bedding as the case may be.
They then begin to incline towards each other at intervals varying from
4 inches to a foot or more in length, and eventually the bent parts meet, thus
enclosing irregular lenticular patches of light-coloured sand. This is as seen
in section parallel to the line of cutting, but similar appearances would
doubtless be presented in a transverse direction, and the lines of ironsand
enclose small masses of material, from which the iron has been removed. In
hardness and friability, and in all respects save colour, due to the presence or

* Penning, Geol. Mag., Dec. II., Vol. III., p. 218.

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LOWER aRBENSAND. 13

partial absence of iron^ the enclosing and enclosed portions are the same, and
the mass can be scraped with equal readiness throughout. But the darker
shell gradually hardens and thickens by further elimination of iron from the
neighbouring sand, both within and around it, but mainly from within, for the
harder the shell has become, the lighter in colour is the nucleus, until it is
found almost a pure white in the complete concretion.

These concretionary lumps may be seen in every stage, and in gradations of
every stage — ^in the earlier the sand presents no alteration except a slight
change in colour, then the shell hardens somewhat and stands out slightly
from the face through weathering. It becomes harder still, and some force is
required to break it ; lastly, it passes into its hardest and thickest form, when
it can be broken only by tne hammer, and when it has removed all iron from
the nucleus, leaving it perfectly soft and white.

This agrees with the conclusions of Mr. Maw that the formation of such
concretions has resulted from segregation independent of chemical combina*
tion or mechanical action.*

Gault.

The Gault, in its extension across the southern midland counties,
forms an almost continuous valley or low-lying plain between the
outcrop of the Lower Greensand and the base of the Chalk escarp-
ment, the uniformity of its level being only interrupted by occa-
sional outliers of newer deposits. In Cambridgeshire, however, the
outlying masses of Chalk and Drift are so extensive that the Gault
plain is broken up into comparatively small isolated areas, and it
is nowhere possible to pass from its upper to its lower line of
boundary in a single traverse across the strike. There are, how-
ever, numerous wells which pierce the formation from top to
bottom, and from them we know that it consists of a stiff bluish-
grey clay, somewhat lighter-coloured and more calcareous in its
upper part, darker and more argillaceous below, while near the
base there is generally a bed of clayey greensand with phosphate
nodules.

As the Gault is traced across Cambridgeshire, its upper surface
is found to have a considerable northerly or north-easterly slope ;
this is partly due to the thinning-out of the formation in that
direction (as will be hereafter explained), and partly to the dimi-
nution in the thickness of the Lower Greensand as it passes
towards the north-east.

It is possible that there may also be a low anticlinal or undula-
tion slightly elevating the beds in the south of the county, and
thus causing a northerly dip towards Cambridge, but we have no
evidence of such an undulation, and the reasons above given are
sufficient to account for the facts observed.

In his paper on " Areas of Apparent Upheaval,"! Mr. Topley
has shown that such deviations from the horizontal are often due
to the thickening or thinning of strata in the direction of dip, and
we see no reason why this should not also be true in the direction
of strike ; thus the rising of the base line of the Gault towards the
south-west is probably due to the concomitant increase in the
thickness of the subjacent Lower Greensand. If, therefore, the
thickening of the Gault itself is added to this, it is clear that its

♦ Quart. Joum. Geol, Soc, vol. xxiv., p. 351.
f Quart, Joum. Geoh Soc, vol. xxx.^ p. 186.

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14 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBBIDGE.

upper surface must have a considerable slope. A diagram (fig. 1 )
>vill make this clear.

Ftg, 1. — Diagram of the Thinning of the Cretaceous Beds along the
Strike from S.W. to N.E.

=r=r^:~--

—— ^-— — ^

LOWER

CHALK.

===fn

CAULT .

LOWER CREENSAWD.

1. Lover Grcensand. 2. Gault.

4. Lower and Middle Chalk.

T. Position of Tring. A. Position of Arlesey.

3. Upper Greensand.
Upper Chalk.

C. Position of Camhridge.

The general decrease of thickness in a hortherly direction may-
be illustrated by giving the average amount of Gault pierced by
wells at various places along the line of strike. Thus between
Arlesey and Ashwell (in Sheet .46) the thickness ranges from 180
to 200 feet ; at Guilden Morden from 170 to 180; between Bas-
singbourn and Barrington its average seems to be 150 or 160, but
it varies considerably (see posted) ; at Haslingfield its thickness is
about 140 feet; near Grantchester and Cambridge it varies between
115 and 130 feet, and in Bottisham Fens from 110 to 120 feet.

Accounts of these and other wells are given in the Appendix.

Besides this gradual attenuation of the Gault, there are also
considerable local variations in its thickness, resulting apparently
from the unevenness of its upper surface, a character which has
probably been produced by the erosion before mentioned. In
some instances the varying amount of sandy beds below the Gault
may account for the differences in the depth of the wells, but there
are usually only a few feet of such sands before the water-bearing
stratum is reached, and where the thickness is considerable we
have generally been able to ascertain its amount, so that this cause
of error is allowed for in the following instances.

Thus while at Morden and Bassingboum the Gault is about
170 feet thick, at the coprolite works near Wendy only 115 feet,
and at King's Bridge near Whaddon it is only 110 feet, but it
rapidly thickens again in a northerlv direction, for wells at Wimpole,
Barrington, and Orwell give a thickness of 170 to 180 feet In all
cases water was found a few feet below the base of the clay, so
that in the intermediate district there would appear to be a large
hollow or depression in the surface of the Gault, bounded on the
north by a long ridge of the same clay, which appears to continue
for some distance eastward, for borings at Shdford and Sawston
found the Gault still about 170 feet thick.

At several localities the thickness of the Gault is found to be
greater where it comes to the surface than at spots in the neigh-

Digitized by VjOOQ IC

GAULT. 16

bourhood where coprolites are being worked ; thus a well in one of
the Gault inliers N.E. of Haslingfield reached water at a depth of
145 feet, whilst another at about the same level, and half a mile
N.E., is 150 feet deep, the upper 20 feet being Chalk MarL This
Marl, therefore, would appear to be the complement of the same
amount of Grault which had been removed to form the hollow from
which the coprolites were being worked out, and where the Gault
below was only 130 feet thick (for descriptions of the pits at this
locality, see p. 37). A repetition of these phenomena is found in
the ridge between Grantchester and Barton, which exhibits flanking
outliers of Chalk Marl (see p, 38). The difference of level is here
easily appreciable by the eye, for the Gault crosses the highest
part of the Barton Road near the third milestone from Cambridge,
and the coprolites have been worked down the slopes in both
directions, the pits near Full Brook being certainly 20 or 30 feet
below this point.

There are several wells in the south part of Cambridge in which
the thickness of Gault is unusually great, being given, indeed, as
160 feet, but we have not been able to obtain any satisfactory
account of them. No less than four wells in Bateman Street,
Russell Street, and Hill's Road are said to have a depth of from
180 to 200 feet, and in these cases great difficulty was experienced
in boring through the beds below the Gault, which presented alterna-
tions of hard and soft strata without water. The depth at which a
supply was ultimately obtained appears therefore to be connected
with some peculiarity at the base of the Gault, which may possibly
undulate and fill up hollows in the Lower Qreensand, as the Chalk
Marl does in the upper surface of the Gault. At Cambridge
station and along the East Road the Gault is shown to be 120 to
130 feet thick in wells, but at Barnwell it is said to be 140 to
150 feet

Any one who stands on the surface of the Gault at Barnwell will
have little doubt about its being higher than the coprolite bed at
Coldham Common, and will see that its slope south-eastward is
much greater than can be accounted for by dip alone ; Coldham
Common, in fact, owes its formation to the existence of a hollow
in the surface of the Gault, which is here only between 110 and
120 feet thick. Moreover the clay lidge or " horseback " has been
disclosed in several pits south of the Newmarket Road, while towards
Fen Ditton its surface slopes so rapidly that coprolites have been
followed below the alluvial level (the Gault under Fen Ditton is
said to be only 108 feet thick). The surface rises again irregularly
about Horningsey, but falls into the hollow of Bottisham Fen.

Beside the class of facts already brought forward, there are
others which point in the same direction : thus, further south-west
the upper part of the Gault becomes very calcareous, and contains
bands of Greensand, so that in Buckinghamshire there is a complete
passage up into the Upper Greensand; but in Cambridgeshire
there are no such sandy beds, and there is no such passage upwards,
the top of the Gault being cut off sharply by an uneven line. All
this indicates that the uppermost beds of the formation (belonging
to the zone of Ammonites infiatv^) are absent over the Cambridge
area. The following diagram (founded on one given in QuaH.
Jofwrn. GeoL Soc^ vol. xxxi., p. 273) represents a method of

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16 GEOLOGT OF THE NEIGHBOURHOOD OF GAKBRIDGE.

roughly estimating the comparative amounts by which the Gault
has been diminished through attenuation and erosion respectively.

Fig. 2, — Diagram of the North-easterly Attenuation of the Gault»

Horizontal sciJe, 20 miles to an inch ; Teitical scale, 400 feet to an inch.
The top line represents the prohable original snr&ce of the Gault.

The curred line bounding the shading represents the present denuded surfiice of

the Gault.

The evidence above set forth regarding the thickness of the
Gault and the irregularities of its surface may be thus summarised :
(1), there is a general decrease in its thickness from S,W. to N.E.,
which appears to be due in part to thinning of the beds, but in
part also to the absence, from denudation, of beds like those which
characterise the upper part of the Gault elsewhere ; (2), there is a
complemental filling up of hollows in the surface of the Gauk by
the overlying Chalk Marl ; this is proved by well sections, as well
as by facts observed in coprolite pits.

From these considerations, together with the evidence afi'orded
by the presence of derived fossils in the coprolite bed (see p. 29),
we cannot but regard the views previously published by one of us
as fully confirmed, namely, that the upper beds of the Gault were
removed from this area by erosion before the deposition of the
Chalk Marl, and that the nodule bed at the base of this marl is the
result of such erosion.

Before proceeding to describe the few open sections which exist
in the area embraced by this memoir, we would point out that the
lower boundary line of the formation is completely hidden for a
long distance under the great western spread of Boulder Clay, and
since there are no good exposures along the remaining part of its
course towards the Fens, the relations of the Gault to Lower
Greensand remain very obscure.

From under the Drift-covered country above mentioned three
barrier-like ridges of Chalk stretch out over the Gault, and, capped
for some distance by Boulder Clay, extend nearly across to the
main mass of the Chalk on the east ; from this, indeed, they are
only separated by the narrow valleys of the Rhee and Cam, these
rivers having nearly everywhere cut through to the Gault below.
Thus the Gault plain is marked out into four separate areas, and
it is only in the northernmost that anything like the whole outcrop
of the formation is exposed.

The southerly district, of which Wendv may be considered as forming the
centre, is limited by the outcrop of the Chalk Marl near the following places,
surrounding it on the N., N.E., and S.E. :— Arrington, Wimpole, Orwell, Har-
rington, Malton near Meldreth, and Whaddon; coprolite pits at all these
places touch the top of the Gault, and at most of them wells pierce through
it to the water-bearing Lower Greensand. In boring wells at Whaddon, and
fdso at Gmlden Morden and Ashwell to the S.W., a second seam of phosphate

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GATJLT. 17

nodules has been fojind at a depth of 60 or 7^ feet below the Cambridge
Greensand ; and at Wendy and Wimpole notice was taken of a third seam of
coprolite^ near the base of theGault ; this probably corresponds to Mr. Price's
zone of Ammonites interruptus, which appears to be very persistent in its range.

Some brick kilns about a mile south of Wimpole expose a few feet of the
clay, but no fossils were foimd.

Crossing the hills by Orwell and Eversden we pass northward into the
second district, which has an average width of about two miles, but contracts
westward between the slopes of" Boulder Clay ; the valley of the Bourn Brook
occupies its central line from Kingston till it joins the Cam at the Old Mills
near Grantchester, northward the ground again rises up to the gravel-capped
ridge which runs through Comberton, Barton, and Grantchester.

The only open section in the area above described is at the brickyard near
the bend of the road, half a mile N.W. of Great Eversden; this is dug to a
depth of about 20 feet in stiff blue clay, but about 8 feet from the surface there
is a thin discontinuous layer of compact red clay, somewhat sand}- and traversed
by annelid borings which are fillea with grey silt.* Some fossils are found,
the most abundant being fragments of Pentacrinus Fittoni ; phosphate nodules
also occur, and among them are forms similar to those in the Cambridge Green-
sand, named Hylospongia and Bonneyia by Mr. W. J. Sollas.

At Haslingfield a well near the church yielded specimens of Ammonites in-
terruptus and phosphate nodules at a depth of 154 feet (water being reached at
157). At Daintrees Inn, however, only a quarter of a mile to the N., about 30
feet of dark sandy clay and sand were passed through before " the rock " was
pierced and a good supply of water obtained. This is an instance of the vary-
mg thickness of the sandy beds at the base of the Gault, for the amount of
clay above is nearly the same in both cases. Near Harlton a seam of nodules
was met with in the Gault at a depth of 56 feet from the surface.
■ 'Passing from this district by Barton, and descending the northern slope of
the ridge towards Cambridge, we enter upon a third plain of Gault which con-
tracts westward into a narrowing valley between the Boulder Clay hills, and
passes eai3tward under th& gravels of the Cam. Northward the ground again
rises towards the road from Cambridge to St. Neots, forming a third ridge,
which doubtless was one capped by the Chalk Marl along its whole length,
but is now bared of its former covering between the foot of Coton Hill
and the high ground occupied by the observatory. There is a brickyard at
the comer of the lane leading to Grantchester (barely a quarter of a mile
eastward of the stone bridge over the Full Brook), where about 16 feet
of stiff dark clay is shoi^tm, containing many scattered nodules of phosphate of
lime (buff coloured outside, but black witnin), decomposing nodules of iron
pyrites, termed " rugg-stones " by the workmen, also occur; Ammonites ros-
tratus and Plicatula pectenoides were the only fossils observed.

Eastward from this pit the Gault passes under the gravels of the Cam valley,
but comes to the surface again as a narrow strip running north and south
through Cambridge, and separating the Barnwell gravels from the lower terrace
on wmch the older part of the town is built. Gault was seen in the foundations
for the new pavilion in Fenners Ground, and thence it a])pears to extend by the
Town Gaol across Parker's Piece and the eastern side of Christ's Piece to New
Square. Clay was again^ seen in the foundations of houses here, and we are
informed that the grealfer part of Maid's Causeway also rests ur»on Gault,
which would appear therefore to occupy part of Bull Green until covered by the
gravel and alluvium of Midsummer Common.

Under Cambridge the zone of Ammonites interruptus has again been proved,
for, According to Prof. Sedgwick "many specimens of Belemnites minimus B,Tid
of broken Ammonites were brought up from out of the lower parts of an old
well sinking near Cambridge." At the waterworks on the Cherry Hinton
Road^ brown clayey sand was found underneath the Gault, containing ferrugi-
nous phosphatic nodules like those found at West Dereham in Norfolk, only
smaller. Again under Coldham's Common about six feet of dark clayey Green -
sand with nodules intervened between the Gault Clay and the hard rock of the

* See note by Prof. T. R. Jones on a similar bed in Kent, GeoL Mag, Dec. II.
Vol.iii. p. 117.

Nd09. ji

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18 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBRIDGE.

Lower Greensand (see Appendix of Well Sections, No. 23). Seams of nodules
are also occasionally met with in the Gault (see Wells, Nos. 25, 71).

At Barnwell there are several brickyards, the clay being worked below 10
or 12 feet of Chalk Marl, from the base of which the "twprolites " have been
extracted long ago. The largest of these belongs to Mr. Bates, and adjoins
the Great Eastern Railway, the section here is as follows : —

feet.
Disturbed Clunch (or Chalk Marl) - - - 10

Gault. Dark slate-coloured clay dnring light grey,
with many phosphate nodules, which are mostly dis-
posed along definite lines, but some are scattered
throughout. PUcatula pectenoides not uncommon - 30 to 40

The " rugg-stones ^' found here are ball-hke masses of a yellowish brown colour
generally hollow or filled with a brown powder, the ferruginous crust contain-
ing numerous small crystals of selenite ; they have doubtless resulted from the
decomposition of nodules of iron pyrites. A large fiat pebble was found in
the Gault here, and is now in the Woodwardian Museum.

The depth of the excavation at Gray's brickyard on the east side of the
railway was about 50 feet in 1875, but it has been dug (according to the fore-
man) to a depth of 66 feet, the day becoming darker in the lower part.
PUcatula pectenoides and fragments of pjrritized wood were obtained here.

At Watfs brickyard on the west side of the Newmarket Road, the following
section was visible in 1875 : —

Feet.
Gravelly soil -----.-2
Chalk Marl (the coprolites being worked out) - - - 12

Gault ; stiff dark clay drying to a light slate colour ; rugg-stones
and phosphatic nodules are common, the latter are sometimes
called ** gault-stones " by the workmen - - - 10

The clay in these pits has a slightly gritty feel, and is used without any
admixture of sand for making the commoner kinds of brick, but sand is added
in manufacturing the better qualities.

On the opposite side of the river, at the corner of the four roads, half a mile
N.W. of Chesterton Church, the same clay is worked, the brickyard being
opened in a ridge-like island of Gault, which here rises above the surrounding
gravel-flats. The workmen stated that they come upon a seam full of phosphate
nodules when they dig down in the winter about 1 / feet.

North of the ridge running between Coton and Cambridge, which forms the
last of the three barriers mentioned in the first instance as crossing the Gault
plain, the surface is much encumbered with, gravels of various ages, but around
Impington the Gault has been denuded of this covering, and the clay is worked
in a brickyard a little eastward of the church. The s^ion was thus noted in
1875:—

Feet.
Disturbed clay, with pockets of gravel * » - - 4

Very hard grey clay - - - - - - 10

Layer containing phosphate nodules (** stony-spit *') - - Oi

Clean dark clay (with fragments of Inocerami) - - - 6

The nodule layer contained many fossils in a more or less fragmentary
condition.

Near Lolworth the Gault boundary advances nearly to that of the Green-
sand ; here, however, the rather sharp slope of the ground narrows the out-
crop of the latter and unduly increases the appearance of unconformity. But
N.E. of Oakington, where the Gault steals over the Greensand, the ground is
almost flat, still the former comes nearly to the edge of the latter. Indeed
there are indications, in the occurrence of Gault fossils on the surface a mile or
two north of this point, that the Gault actually overlaps the Greensand, and
rests or has rested durectly on the Oolitic Clays; but lithologically the clays

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GAtTLT. 19

are too much alike to render this point certain in the absence of palseontological
evidence. About a mile and a half to the N.W. from Impington the base of
the Gault is reached^ and in tracing its boundary line across the fields evidences
of the basement layer of phosphate nodules were occasionally met with. Thus
between Landbeach and Cottenham many coprolites and fragments of Belem-
nites ultinms are scattered over the surface of ploughed fields^ or may be seen
in the sides of newly cut ditches. The same is the case in the fields north of
the road to Cottenham, near the deep ditch which drains this district ; Ammonites
interruptus occurred among the fragments picked up here, and the layer maybe
traced towards Goose Farm till it passes beneath gravel.

There is yet another area where the Gault appears, under somewhat different
conditions, viz., in the Fen district east of the Cam*

A quarter of a mile south of Clayhithe, just above the alluvium, a small
brickyard gave the section : —

Gravelly soil; with pockets of sand and disturbed Gault below,
containing flints and also coprolites from the Greensand out-*
crop above ------- 3-4 feet.

Grey Gault, with a few phosphatic nodules - - - 6-8 „

An Ichihyosattr vertebra was obtained here, and other fossils are said to be
found occasionally.

Eastward from this point the Chalk Marl comes on and underlies the whole
of Homingsey and Ing fens; the coprolites, however, crop out again near Bottis-
ham Load, and N.E. of this the Gault again forms the substratum. By the
Load and half a mile N.W. of the village is a small brickyard, and at another
near SwafiPham Load a new cut gave the following section : —

Peat, underlain in places by pockets of clean yellowish-brown
sand, so pure as to be used in the brickmaking - - 2 feet.

Greyish-blue Gault, with scattered phosphate nodules, a band
of them occurring at a depth of 12 feet according to the
workmen - - - - - - -8„

Another small brick-pit, in the Fen about half a mile to the west of this,
shows a similar section.

Inliers.

^ These form an interesting study as they are all produced by local banks or
ridges cutting out the Chalk Marl above, and most of them would probably
have escaped observation had they not been disclosed by the search after copro-
lites. Particulars concerning them will be found further on in the description
o£ the coproUte bed, but the positions of the most important may be here
indicated. There are three Gault inliers in the outlier of Chalk Marl, north
of Hashngfield, and two more under the gravel near Hauxton Mill Bridge.
Again near High Hall Farm at Homingsey there is an inlier of considerable
extent cutting out the coproHtes. The workmen term these patches "dead
ground," in consequence of the coprolite bed running " dead " all round them,
on the same principle as the name Rothetodteliegende is given to a division of
the Permian in Germany.

B 2

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20 GEOLOGY OP THE NEIGHBOURHOOD OP CAMBRIDGE.

CHAPTER IV.-THE CHALK.

General Description and Classification.

This formation, which occupies so large a portion of our area,
has not hitherto received the attention it merits at the hand of
geologists. The coprolite bed which forms its base has indeed
been minutely studied, and the Cherry Hinton Chalk quarries are
known to every student of geology at Cambridge ; Prof. Seeley
and Prof. Bonney have briefly noticed the lowermost beds seen in
this and other pits near Cambridge,* but nothing like a full
account of the Cambridgeshire Chalk has yet been written. We
hope that the iniformation contained in the following pages will to
a great extent supply this deficiency, for we have found it possible
to institute a more minute subdivision, and to give a more complete
description, of the beds composing the lower and middle portions of
the formation than has hitherto been attempted by Englisli
geologists except in more limited areas.

The classification we propose is founded upon a consideration
both of the lithological and the palaeontological characters of the
strata, it combines the results of observation in the field and of
study in the museum. But it must be understood that this exa-
mination has been by no means exhaustive even in the area we
have examined. It was not until the larger portion of this had
been surveyed that we became convinced of the value and persis-
tence of the divisions, and we have not had any opportunity of
following them beyond the limits of the map. (Frontispiece).

From a comparison, however, of our own work with the results
obtained by other observers, we feel certain that not only is the
existence of zones in the Chalk a well ascertained fact, but that
they are remarkably constant throughout the whole extent of the
escarpment from Dorsetshire to Cambridgeshire. (See p. 137.)

Mr. Whitakee has briefly described the diflferent lithological
characters which the beds of the Lower Chalk present in Bucking-
hamshire; t and Dr. Baerois has shown that the palaeontological
zones, which had been established by Prof. Hebeet and himself in
the North of France, were similarly developed in England. The
table (p, 21) will indicate how far our divisions agree with those,
of the above-mentioned writers.

With regard to the larger divisions under which the succession of
zones may be grouped, we have felt it desirable to revive the
general classification proposed by Dr. S. Woodward in 1833 for the
Chalk of Norfolk. The Melbourn Rock and the Chalk Rock
form such marked breaks in the series that it naturally falls into
three main divisions, lower, middle, and upper. We may point
out that these exactly correspond with those termed by D'Orbigny,
Cenomanien, Turonien and Senonien, as they are defined by Dr.

* Seblbt, Geol, Mag., vol. i. p. 152, and Bonnet's Cambridgeshire Geology, p. 48.
t Quart, Journ, Geol, Soc,, vol. xxi. p. 398, and Mem, Geol Survey, vol. iv.
pp. 40, 44, and 49.

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CHALK.

Barrots.* The lowermost Chalk has been separated by some into
Grey Chalk and Chalk Marl ; following Mr. Whitaker we regard
as Chalk Marl that only which underlies the Totternhoe Stone, and
we agree with Mr. F. G. H. Price f in using the term Grey Chalk
for the remainder of the division.

Table of Chalk Zones.

Whitaker, 1865, 1872
(Bedford and Bucks).

Classification for
Cambridgeshire,

1878.

Barrois, 1876
(Berkshire and
Oxfordshire).

-^ r

o J
f* 1

o L

White chalk with flints i

Chalk rock

White chalk, with few
flints, but with thin
layers of marl, 350^
feet.

Hard bedded chalk with
thin marly layers.

Blocky chalk with curved
bedding, 60 feet.

Totternhoe stone, 10-
15 feet.

Totternhoe marl, 80 feet

Zone of Micraster
cor-bovts.

Chalk Rock

Zone of Terebratu-
Una gracilis, 150
feet, in two divi-
sions ; the lower.

Vandlebury beds -

Zone of Rhyncho-
nella Cuvieri,60-
70 feet.

Melboum rock

Zone of Holaster
subglobosus, 80
feet.

Totternhoe etone,
15 feet.

Zone of Rhyncho-
nella Martini^ 50-
60 feet.

Cambridge Green-
sand.

Zone a Micraster
cov'bovis.

Zone h Holaster
planus, 6 to 10 feet.

Zone a Terebratula
gracilis, 90 feet.

Zone Jfc Inoccramus
. labiatus, 60 feet.

Zone a Belemnites
plenus (not identi-
fied in Berkshire).^

Zone a Holaster
I subglobsus, 150
feet (in three
divisions).

? Chloritic marl.

From this it will be seen that we have recognised a greater
number of zones or subdivisions than had been previously proposed,
the reason of this is that we have acknowledged the existence of
{ everal bands of rock which exhibit a marked lithological contrast
to the other beds of chalk, and separate zones containing different
groups of fossils.

Although these rock-beds are probably only subsidiary to the
palaeontological zones, and were doubtless formed during the time

♦ Recherches sur les Terrains Cretac^s superieurs de TAngleterre et de Tlrlande.
f Quart, Joum. GeoL Soc, vol. xxxiii. p. 431.

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22 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

that the conditions of the deposit were changing, we wish to call
special attention to them at the present time as they afford the only
means by which the zones can be satisfactorily traced across the
country.

The ToUemhoe Stone is the lowest of these bands of rock, and its
true position was first recognised in Beds and Bucks by Mr.
Whitakee in 1865. Although it is one of the best marked horizons
in the whole mass of the Chalky it possesses no very distinctive
palseontological characters ; it contains few fossils that are not found
either above or below, all that can be said is that fossils are indi-
vidually more abundant at this horizon, and that certain species
seem here to make their first appearance.

The Melbowrn Rock, the second of these beds, seems to be of even
more constant occurrence than the Tottemhoe Stone, since it is
found throughout the southern counties where the latter does not
seem to be everywhere lithologically represented. In Cambridge-
shire it always exhibits one or more layers of laminated marl
separated by beds of hard rocky cream-coloured chalk ; its fauna is
scanty, crushed Bhvnchonellce and OstreoB being the most abundant
fossils, and even tne characteristic Belemnite appears to be less
common than in more southern counties.

The beds for which we have suggested the provisional name of
VavMehv/ry Beds are not often seen in section, and may not form
so important and persistent an horizon as the others ; there appear,
however, to be similar hard beds in the Dover Section, about the
same height above the zone of BeUmnites plenus,* Where seen
these beds present characters which reseipble those of the Chalk
Rock. They have not yielded any remarkable fossils, but Bhyn-
chonella Cumeri and Inoceramtis problematicus are generally common.

The Chalk Bock, the fourth of these rocky bands, and perhaps
the most conspicious of anjr, was the earliest to receive notice in
England, f Its fauna, which is worthy of detailed investigation,
appears to contain a mixture of Upper and Middle Chalk forms
together with some that may be peculiar ; amongst the last are
several Gasteropods. Lists of its fossils have been printed by
Mr. E. C. Davey, of Wantage, and in VoL IV. of the Memoirs ot
the Geological Survey.

As the Cambridge weensand, the Chalk Marl, and the Totternhoe
Stone have been mapped over the country to the S.W., we can
pursue the usual plan in treating of these beds, describing the
sections from west to east; but for all the divisions above the
Tottemhoe Stone it will be more convenient to commence the
description of each zone where it is intersected by the line of
section (Plate 5), and having indicated the exposures of similar
beds along the outcrop towards the S.W. to return to the starting
point and trace the zone to the N.E.

Such outliers as we have recognised to belong to any of the
divisions will be mentioned after the main outcrops have been
described.

♦ See Memoirs of the Geological Survey, vol. iv. p. 32.

f Catalogue oj Hock Specimens id the Museum of Practical Geology. Ed. 2,
1859, See also Quart, Journ. Geol. Soc. vol. xvii. p. 166, and Mem. GeoL Surv.
fol. iv. p. 46.

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CHALK MARL. 23

Mr. Allen succeeded in making a considerable collection of
fossils from localities indicated by ourselves, and thus supplied us
with the material for the lists of fossils given in the following
pages. In the case of the Cambridge Greensand and Totternhoe
Stone, however, this has been supplemented by means of fossils iii
the Woodwardian Museiun.

LOWER CHALK.

Chalk Marl.

The Chalk Marl forms a low undulating strip of ground, varying
in breadth according to the slope of the land, between the irregular
outcrop of the Gault and that of the Totternhoe Stone, -which forms
the base of the Grey Chalk. It lies for the most part on the
eastern side of the Cam and Rhee Valleys, and has been traced
from the neighbourhood of Ashwell, in Sheet 52, through the N.W.
comer of Sheet 47, and into Sheet 51 as far as Reach and Burwell
on the borders of the Fen country.

There are, however, numerous outliers to the westward of
this line, and one of these occupies a considerable area in the
south-western comer of Sheet 51 ; this may, indeed, be connected
with the main mass by a narrow neck of marl near Harston,
where a depression in the surface of the Gault allows the
" coprolite bed " to pass below the level of the alluvium, but the
river Rhee cuts down to the Gault, both above and below this

foint, so that the tract above mentioned is practically an outlier,
rom Harston it widens out by Barrington and Haslingfield, and
the higher central portion of the ridge is formed of Grey Chalk
capped with Boulder Clay ; the whole extends westward between
Wimpole and Eversden, and stretches into Sheet 52, where it must
underlie the glacial clay for several square miles.

The coprolite bed which forms the base of the Chalk Marl has

been worked along the whole length of its outcrop, and all round

the above mentioned outlier ; several outlying patches, with more

r less of the overlying marl, are to be found in the neighbourhood

of Wimpole, Orwell, Barrington, and Haslingfield.

The ridge-like outliers to the northward, west of Grantchester
and Cambridge, have already been mentioned in describing the
outcrop of the Gault, and these likewise stretch westward under
the Boulder Clay of Madingley and Hard wick ; they are clearly
the remnants of an extensive promontory of Chalk Marl which
occupied the west side of the Cam valley in Pre-Glacial times, but
which has been broken up and removed by Post-Glacial erosion
and denudation.

There is always a considerable quantity of water in the lowest
part of the Chalk Marl held up by the Gault below, but no strong
springs are thrown out like those from the overlying Totternhoe
Stone.

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24 GEOLOGY OF THE NEIGHBOURHOOD OP CAMBRIDGE.

The Cambridge Greensand.

Character and Mode of Occv/rrence.

This basement bed has long been known by the name of the
" Carri bridge Greensand " or '* Coprolite Bed." It is a clayey marl,
to which a greenish colour and a sandy texture is imparted by the
presence of numerous Glauconite grains, and its lowermost layer
always contains an accumulation of the phosphatic nodules, com-
mercially known as '* coprolites/'

The Cambridge Greensand has been traced north-eastwards from
Harlington in Bedfordshire into Cambridgeshire, and has every-
where been found to pfresent similar characters. Its constitution
varies slightly in different places according as one or other of its
several ingredients, clay, marl, or glauconite, happens to prepon-
derate, but everywhere the green grains become fewer and fewer
in an upward direction, so that it gradually passes into the greyish
beds of the Chalk Marl.

For a long time it was considered as Upper Greensand, and
was supposed to be the diminutive representative of the series of
greeusands, chert-beds, and firestones so well known in the south
of England; it has been shown, however, that these die out in
a northerly direction before the Cambridge Greensand com-
mences,* and it is much more probable that this is the homotaxial
equivalent of the so-called Chloritic Marl, which is generally
separated from the Upper Greensand by a band of phosphatic
nodules, t The earliest notice of the bed is by Prof Hailstone in
1816,t who describes the section in the brick pits near Castle Hill
as exhibiting a passage from Marl through Greensand to the Gault,
and speaks of the coprolites as "irregular dark brown nodules of a
ferruginous indurated marl."

In 1836, FiTTON remarked,§ "This formation here differs from
that of some of the more southern counties in its much smaller
thickness, in the absence of chert, and the comparative rarity of
green particles which are here confined to a stratum not more than
18 inches thick, by which the lowest beds of the Chalk are sepa-
rated from the Gault, as is well seen in the section exposed at the
Castle Hill, Cambridge. The presence of this green bed, however,
is remarkably constant, and it contains many fossils, some of which
are common to this formation and the Chalk ; but others, at least
in this country, are confined to the sand." In this observation
Dr. FiTTON anticipates the subsequent division of its fauna into
Chalk and Gault elements.

In 1845 Prof. Sedgwick describes the bed "as only a few inches
thick, and above it there is sometimes an ambiguous deposit of a
few feet which forms a passage into the Lower Chalk. It is not
true, as has formerly been stated, that the Chalk Marl forms a
passage into the Gault, for the Upper Greensand makes a natural
break between them."||

* Jdkes-Browne, Quart. Joum, GeoL Soc, vol. xxxi. p. 256.
t ToPLEY, Geol. Survey Memoir on the Geology of the Weald, p. 157, and
Barrois, Recherches sur les Terrains Cretaces Superieurs.
J Trans. Geol. Soc.^ vol. iii. p. 243.
§ Trans. GeoL Soc, part 2, Vol. iv. p. 306.
11 Hep. Brit. Assoc. 'Trans., Sections, p. 40.

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CHALK MABL. 25

This remark is very true; there never occurs anything like a
passage from the one formation into the other ; on the contrary,
the Une of demarcation between Gault and Greensand is always
sharp and clear, and the surface of the Gault is frequently uneven,
exhibiting hollows and undulations which have evidently been pro-
duced upon it before the deposition of the overlying nodule bed.
All succeeding observers have noticed the existence of these
irregularities,* and their influence on the outcrop of the bed is very
plainly shown by the line on the Geological Survey map, which
does not at all follow the contour of the land, but rises and falls
perceptibly within very short distances.

The numerous small outliers and patches which exist every-
where on the borders of its outcrop, aad consist of the coprolite
bed with more or less of the overlying marl, almost always rest in
hollows of the underlying Gault, and it is doubtless to this circum-
stance that they owe their preservation.

It is worthy of remark that the coprolite bed, as such, i,e., en-
closing phosphatic nodules, never occurs quite at or even near to
the surface. When the bed rises to within about three feet of the
surface, it ceases to be continuous, and lies in hollows, which are
generally steep-sided, and resemble " pot-holesJ^ An area contain-
ing coprolites is more valuable when they '^' lay fleet '' (within a
short distance of the surface), because less expensively worked,
than when they occur at a considerable depth.

The nodule bed itself rarely exceeds a thickness of 10 inches,
but the Greensand or Glauconite Marl generally extends upwards
for another 6 or 6 inches ; when, however, there are any undula-
tions in the surface of the Gault, the stratum of Greensand is
always seen to be thinner on the top of the rolls, and thicker in the
hollows, being frequently from 18 to 24 inches deep in the latter.
The same is generally the case with the layer of phosphatic
nodules ; in some few instances it appears to exhibit little difference
in thickness, but as a rule there is a greater accumulation in the
troughs, and occasionally it is entirely absent on high rolls or
ridges.

Included Erratics.

Another proof of the existence of currents during the depo-
sition of the Cambridge Greensand is the frequent occurrence of
extraneous rock fragments in the bed, which are sometimes so large
as to cut out the nodule seam altogether. Their existence was first
pointed out by Prof. Seeley, in his paper on the " Rock of the
Cambridge Greensand,"t and he notices some of the varieties which
occur as well as the angular outline, which they often present. A
large number of these stones and erratics were subsequently collected
and placed in the Woodwardian Museum, and some were described
in a paper read before the Geological Society in 18724 Among
them are fragments of granite, basalt, hyperite, gneiss, quartzite,
schist, sandstone, and purple grits, many resembling Scotch and

♦ Seelby, GeoL Mag., vol. lii., p. 306 j Jentns, Proc. Bath, Nat, HisL Club,
Tol. i., p. 9. Bonnet, Proc, GeoL Assoc, vol. iii., p. 14.

{Geol. Mag,, vol. iii., p. 303.
SoLLAS and Juxeb-Bbownb, Quart, Joum, GeoL Soc,, xxix. p. 1 1.

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26 aEOLOGY OF THE NEIGHBOURHOOD OF CAMBEIDGE.

Norwegian rocks, and the authors maintained that the agency of
ice must be called in to account for the presence of so many
stones and angular blocks at so great a distance from their parent
masses. Prof. Bonney had also come to the same conclusion
regarding them.* Two specimens more recently obtained are thus
described by Mr. Rutley. (1.) A quartz porphyry, with a compact
pink felsitic matrix containing porphyntic blebs of quartz and
decomposed crystals of felspar, probably orthoclase. (2.) A dark
grey aphanitic rock with a few porphyritic felspar crystals, probably
a felstone, but may be a basalt. With these are fragments of
granite and red schistose sandstone, and a lump of pinkish talcose
schist, nearly as soft as soapstone. In all some 30 frfigments, large
and small, were collected in 1875 from coprolite pits near Cam-
bridge.

Nature of the Copr elites.

The nodules themselves are usually dark brown or nearly black
outside, but internally of a creamy grey or light brown ; amongst
them there are some few of a dull buff, which probably do not
contain so much phosphate of lime as the darker stones. A good
aggregate sample of Cambridge coprolites contains from 56 to 58
per cent, of this phosphate, and they are consequently richer than
the Neocomian nodules, which seldom average above 50 per cent,
and better than those found in the Red Crag, which vary greatly,
but generally contain from 52 to 56 per cent of the phosphate.

Ordinary commercial analyses of coprolites often indicate a
higher percentage than the above, but Dr. VoELCKERf explains that
when the amount of phosphate is determined in the usual way by
precipitation, the fluoride of calcium which the nodules contam is
thrown down with the precipitate, and consequently the amount of
tribasic phosphate of lime is stated 3 or 4 per cent higher than it
is in reality. Dr. Voelcker has therefore ascertained the true pro-
portion of this phosphate in several samples by determining the
percentage of phosphoric acid, and calculating the amount of
^'hone earth^^ or tribasic phosphate to which this acid is equivalent
We append three of the detailed analyses thus made* : —

Moisture and organic matter - - .

Lime -----_
♦Phosphoric acid - - -. - -
fCarbonic acid - . - - _

Oxide of iron - - - - -

Alumina and magnesia, &c.

Sulphuric acid, fluorine, &c. - - »

Insoluble siliceous matter - - - -

4*01
45-39
26-75
5-13
1-87
4-62
6*01
6-22

3-52
46-60
27-01
5-49
2-08
2-47
6-79
6-04

3-80
43-68
26-05

ll8-70

7-77

.100-00

100-00

* Equal to tribasic phosphate of lime

tE(iual to carbonate of lime - - „

57-12
11-66

58-52
12-47

56-87

* Proc, Geol. Assoc., vol. iii., p. 18, and Cambridgeshire Geology, p. 33.

f Joum. Bog. Agric. Soc., vol. xxi., p. 358.

X See Joum. Hog. Agric. Soc, vol. xxi. p. 358, and ser. ii., vol. xi. p. 404.

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CHALK MABL.

The analysis originally quoted by Prof. Seeley, and subse-
quently by Prof. BoNNEY, contains less than the ordinary amount
of phosphoric acid, viz., 25*29 only, equal to 54*89 of the phos-
phate ; another more recently made by Dr. Voelcker, yielded an
unusually large amount, equal to 63'60 of the phosphate, so that
the quality of the nodules is found to vary considerably.

We have elsewhere remarked upon the similarity between the
Cambridge nodules and those which occur in the upper portion of
the Gault; it is satisfactory, therefore, to find that their chemical
composition is identical^ and that the amoimt of phosphate of lime
averages nearly the same in samples from both formations. We
have been furnished with the following analyses of Gault phos-
phates ; the first two are from the Lower Gault of Bedfordshire,
and for them we are indebted to Mr. J. B. Lawes, of St Albans ;
the third is a sample from the nodule bed in the Upper Gault at
Slapton, Bucks, and was supplied by Mr. W. Wilkerson, of Leighton
Buzzard

L-Bj
Dr. Voelcker.

II~By
Mr. B. Dyer.

in.-By
Mr.A. Sibson.

Moisture and organic matter
Tiime - - - _
♦Phosphoric acid - - -
Oxide of iron, carbonic acid, alumina,
mafjnesia, &c. - - -
Insoluble siliceous matter

3-79
46-13
27-68

17-76
4-64

5'85
44-44

27-27

16-01
6-43

•68
46-11
30-04

17-04
6-13

♦Equal to tribasic phosphate of lime -

100-00
60-43

loo-eo

59-53

100-00
65-58

In comparing the two sets of analyses it must be remembered
that the latter were only made for commercial purposes, and con-
sequently that the calculated amount of tribasic phosphate is
greater than the reality, for the reason given before; if due
allowance be made for this it will be ^een that the actual amount
would average about the same in both cases.

Origin of the Nodules,
As regards the mode in which the phosphatic nodules have
originated, it may be remarked in the first place that a consider-
able proportion of those in every washed heap can easily be recog-
nised as fossil organisms. The bones and teeth of reptiles and
fishes, and the casts of MoUusca, Crustacea, Echinoderms, and
Corals, speak for themselves, though all these are often worn,
broken, and fragmentary ; of the rest many have recently been
proved to be phosphatised sponges,* and we fully believe that all,
in common with other phosphatic nodules, have originated in the
decomposition of organic matter on the sea bottom. It is known
that phosphate of lime is soluble in carbonated water, and that
from such solution it is precipitated by ammonia, which is one of
the products of the decomposition of animal matter ; it seems most
probable, therefore, that such phosphate as is contained in the

* SOLLAS, Quart, Journ, GeoL Soc.y vol. xxix. pp. 63 and 76.

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28 GEOLOGY OF THE NEIGHBOUBHOOD OF CAMBRIDGE.

water permeating the mud of a uballow sea-bottom should be con -
centrated at those points where ammonia is being evolved.*

Many facts have been noticed showing the connexion between
decaying animal matter and the formation of the calcic phos-
phate ;t the under surfaces of Crustacea, for instance, are gene-
rally covered with phosphate^ while the carapace is free from it;
the calyces of Corals are often filled up m a similar manner,
and the bases of sharks' teeth are sometimes completely embedded
in the mineral, while their polished surfaces are clean and free.

In these cases and in others where some shell happens to have
been entirely enclosed in a nodule, the hard parts remain as an
evidence of its mode of formation, but when the decaying organism

Eossessed no hard test or skeleton an entirely amorphous and
omogeneous nodule would be the result.

On this subject some remarks by M. L. Geunee on the phosphates
of the Perte du RhoneJ may be translated as being in some
measure applicable to those from the Cambridge Greensand ; he
says : — " W hen the aperture of the shell communicating with the
exterior is narrow, as in the small Echini and the inner chambers
of Cephalopoda, the cast consists of a dense and compact homo-
geneous mass, composed of an intimate mixture of phosphate and
carbonate of lime ; the tint is then a clear blonde or yellow brown,
more rarely black, according to the proportion of organic matter
mixed with the phosphate."

** On the contrary, when the communication with the interior of
the shell is easier, the cast is more or less filled with grains of
black or green sand; this is the case with the large external
chambers of Cephalopoda, with many Gasterpods and with Bivalves.
The amount of phosphate is then also more or less diminished,
and this is also the case when the calcareous shell is relatively
thick." Four of the analyses upon which he founds this opinion
are given below : —

Calc. Phosph.

Calc. Carb.

Glauconite.

r Echinus ...
\ Nautilus (inner chamber)

' Ammonite (large fragment) -
' Inoceramus - - -

70-60
65*30
46-20
38-25

17-40
29-60
22-80
33-55

12*00

5-00

31-00

28-20

From these data he concludes that the phosphate must have
come from without in a state of solution, and cannot have been
introduced in the form of a soft paste through the orifices of the
shell or test, since *' we should then find the green grains of the
encasing sand constantly present instead of their being only in the
more open ghells." He attributes the production of these phos-
phate beds "to the prolonged accumulation of the remains of
animals which lived and died upon the spot."

* See Bonnet, in Proc. Geol. Assoc, vol. iii. p. 14.

t See Geol. Mag., vol. x. pp. 269, 270, and Quart. Journ. Geol, Soc, voL xxix.
pp. 54, 60.

J Bull, Sac, Geol. de France, ser. ii. t. xviii. p. 62.

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CHALK HABL. 29

As regards the Cambridge phosphates it is certainly the case
that the casts of Echinoderms, small Gasteropods, close-fitting Bi-
yalves, and the chambered portions of Cephaiopods afford the most
compact and homogeneous phosphatic substance, while green
grains occur in that which occupies the larger Bivalves^ the calyces
of Corals^ and the more open parts of other organisms.

Such facts likewise negative the possibility of the phosphate
having been subsequently introduced after the formation of the
deposits, and Mr. Nesbit's analyses of the nodules from the
Chloritic Marl in the Isle of Wight, showing that there is always
more calcic phosphate in the interior of a nodule or cast than
there is in the outer part, confirms this conclusion.

It must not be supposed, however, that the nodules of the
Cambridge Greensand nave originated in the bed where they are
now found. We have already noticed the absence of the upper
beds of the Gault in Cambridgeshire, and also the evidences of
erosion which its surface presents. These circumstances, taken in
conjunction with the waterwom condition of most of the ** copro-
lites," and the fact that the majority q{ the fossils belong to
Gault species, lead to the conclusion that they have been derived
from the underlying formations. Moreover, the nodules them-
selves, both dark and light coloured kinds, are exactly similar to
those found in the nodule beds of the Upper Gault, or zone of
Ammonites rostrattts^ in Kent, Surrey, and Buckinghamshire ;
these beds always contain a quantity of glauconitic sand, so that
the presence of green grains in some of the Cambridge phosphates
offers no difficulty to the acceptance of such a derivation.*

Fossils.

We are thus brought to a consideration of the fossil contents of
the Cambridge Greensand, which are divisible into two groups,
exhibiting marked differences in their palseontological affinities as
well as in their states of preservation and fossilization, the one
group of fossils has been derived from the Gault, the other is
proper to the bed itself.

The large derived fauna, comprising upwards of 200 species of
invertebrata, together with many reptiles and fish, was for a long
time looked upon as indigenous to the formation, and its members
were catalogued as Upper Greensand forms ; as such an assignment
involves a double error, and as they properly belong to the Upper
Gault, or zone of Ammonites rostratus, they should be considered as
representing that zone in Cambridgeshire, and not as belonging to
any equivalent of the Warminster Greensand or of the Chloritic
Marl. A full list of these fossils will be found in the 'Appendix.

The following is a list of the fossils which appear to belong to
the glauconitic marl itself, and most of these range upwards into
the Chalk Marl of Cambridgeshire and other counties : —

List of Fossils from the Cambridge Greensand.

Acanthopholis eucercus, Seeley.

M stereosaurus, Seeley,

* See F. G. H. Foice, Quart, Joum, Geol, Soc,, toI. zxz. p. 853, and Jukes-
Buown, lifid, Tol. zxxi. pp. 270, 271.

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Biiiim i

30 QEOLOGT OP THE NEIOHBOUBHOOD OF GAMBBIDGE.

Anoplosaunis curtonotus, Setley. .

„ major, Seeley.

IchtbyowuruB campylodon. Carter,
Macrurosaurus semnus, Seeley.
=* Acanthopholis platypus, Seeley,
Omithocheirus Garten, Seeley.

„ Fittoni, Owen.

Plesiofiaurus (several species).
Polyptychodon interruptus, Owen,
Testudo cantabrigiensis, Seeley (M.S.)-

Edaphodon Sedgwickii, Ag,

Enchodus halocyon, Ag.

Notidanus microdoD, Ag.

Otodus appendiculatus, Aa,

Protosphyraena ferox, Leidy (Saorocephalns lanciformis, Harlan)*

> Belemnites ultimns, lyOrb.

Anomia transversa, Seeley.

4 Avicula gryphseoides. Sow,

lima globosa Shy,

„ omata. Ether.
Ostrea cunabula, Seeley.

„ frons, Park.

„ lagena, Seeley.

„ vesiculariB, Sby.

„ (Exogyra) baliotoidea, Sby.
Pc^n orbicularis, Sby, I

Plicatula inflata, Sby, I

„ minuta, Seeley, I

,, sigillina. Woodward. I

Radiolites Moretoni, Mant.
Teredo amphisbsena. Gold/,

Argiope megatrema, Sby,
Kingena lima, Defr,
RhynchoneUa lineolata, PhU,

„ mantelliana, Sby.

Terebratula biplicata, Sby.

„ semiglobosa, Sby.

„ sulcifera, Morris.
Terebratulina rigida, vsr,

„ striata, WaM,

„ „ var. triangularis, Ether.

Theci(Uum Wetherellu, Morris.

Astro|^nium, sp.

Cidans Bowerbankii« JFbr^es (spines).

„ Dizoni, Cotteau (iq^ines).

„ gradataj Seeley.

f, Sedgwickii, Seeley,

„ vesiculosa. Gold/, (sjanes).

* It is much more difficnlt to separate the derived Vertebrate remains from the
others, than it is in the case of the Invertebrata, and it may be that more species
will have to be added to the above list. The bones and teeth of Ichthyosaurus often
occur in associated sets, and in a friable condition, hardly miQeralised ; many of the
Dinosauria have also been obtained in associated series, and these bones are generally
preserved in a very light-colonred phosphate ; such remains may certainly be
regarded as belonging to the bed ia which they are found.

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..«4 _.M—

CHALK MARL. 31

Discoidea cylindrical Lam,
„ subucula, Klein.
Echinocyphxis impressus, Seeley,
Goniophorus lunatus, Ag., var minutus, Seeley.
Holaster subglobosus, Leske.
Fentacrinus Fittoni, Austen.
Salenia Woodwardii, Seeley,

Palaega Carteri, Woodward,
Pollicipes arcuatum, Dar,

„ glaber, Sby,

„ unguis, Sby,
Vermicularia umbonata, Maiit. (var. of).
Micrabacia coronula, Goldf,
OnchotrochuB Carteri, Duncan.
Fharetrospongia Strahani, Sollas,
Parkeria (large species).

Description of Sections.

In describing the sections presented by the various "coprolite
pits " which came under our notice, it will be convenient to treat
firstly of those occurring along the main line of outcrop from S.W.
to N.E,, and secondly, of the outliers which lie to the W. and N. W.
of this line, on the opposite side of the continuous valley formed by
the Rhee and Granta ; including under the latter head the peninsula-
like mass stretching westward from Harston and Haslingfield.

Main Outcrop,

The nodule bed, forming the boundary line of the Chalk Marl enters
Sheet 47 half a mile S.W. of Bleak Hall, near Bassingbourn, and passes into
51 S.W. by the 42nd milestone on the Roman way called Ermine Street, west
of Whaddon. There are still many workings in the neighbourhood of Bas-
singbourn and Whaddon, but none called for special remark till we reach
King's Bridge North of the latter place, where the bed has been followed
10 or 12 feet below the level of the alluvium on each side of the stream,
although both westward and eastward of this spot its banks consist of Gault.
The same was found to be the case near Malton Farm, and thus the extreme
unevenness of the surface on which the nodule-bed rests may be perceived
from a mere inspection of the map. The irregularity of the line further N,E.
testifies to the same fact, for it runs in and out without conforming in any way
to the contours or natural features of the country ; its behaviour is in fact the
direct result of the hollows and ridges existing in the surface of the Gault.

Near Harston ,the coprolites have been extensively worked, and are now
exhausted from the land on the eastern side of the river ; a pit in the field
S.W. of Hauxton Mill Bridge showed the following section in 1876 : —

Feet.
Evenly bedded sand and gravel - - 3 to 10

Grey marly chalk (" clunch ") - - 12 to 6

Greensand bed, with " coprolites " - - 1

A few yards to the westward of this pit the basement bed had cropped
out round a patch of dead "ground," which thus formed an inlying ridge of
Grault (beneath a thin covering of gravel) about 20 yards broad from north tu
south, and not more than 100 yards long. The bed has also been worked on
the east side of the road, and the workmen stated that there was a similar
small patch of ddad ground on this land. North of Hauxton Bridge the
coprolites have been worked out for some distance, but nearer Trumpington
we believe they have not yet been disturbed, and the outcrop passes beneath
the gravel forming the right-hand bank of the river near " Byron's Pool."

North of Trumpington, on Major Pemberton's property, the phosphate bed
has been worked for many years, the trench which was open in 1875 ran nearly

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32 GEOLOGT OF THE KEIGHBOUBHOOD OF OAMBBIDGE.

N. and S. at a distance of about a quarter of a mile from the mun road, and
the ordinary depth was from 18 to 20 feet, but the surface of the Gault was
gently undulating and towards the northern end rose up in a large roll which
brought the nodule seam to within 13 or 14 feet of the surface of the ground.
The general direction of this ridge was N.W. and S.E., and the foreman
stated that it had continued since they first opened the pit (a distance of about
150 feet when these notes were taken), but its height had been gradually
diminishing as the trench was cut back eastward. The seam of Greensand
was certainly thinner on the top of the roll, while in the hollow on one side
the dark sandy marl formed a tolerably well-marked bed nearly two feet thick,
the lower half being full of the black phosphate nodules, in other places the
thickness of the sandy seam was not more tnan one foot, only 8 or 9 inches of
this being occupied by the nodule bed. Thus the general section was as
follows : —

Feet.
Greyish-white clunch^ with irregular pockets of gravel

2 or 3 feet deep - - - - - 6

Dark grey clunch (lumpy) - - - - 12

Dark glauconitic marl with nodules - - - 1

Marl with coprolites was seen in the ditch or watercourse just south of Mr. . . 's
farm, and the outcrop of this bed must pass under the gravel across the road
from Trumpingion to Cambridge, near Willer's Nursery ; in 1876 a pit was
opened near Vicar's firook, a little south of the point where it crosses the road,
and the section shown was the following : —

Feet.
Fine gravel and sand - - - - - 6

Clunch, wet and dark-coloured - - - - 8

Marly greensand, looking dark and muddy - - 1

There were strong springs at the base of the gravel, and much difficulty was
experienced in pumping out the water.

In 1875 a trench was made for the purpose of laying a drain between the
New Pavilion in Fenner's Ground, Cambridge, and the main pipes in Hills
Road, this intersected a narrow tongue of marl with coprolites, as shown in
fig. 22, p. 102.

The main line of outcrop must therefore run by St. Paul's Church, and
across the fields to the cemetery ; N.E. of this the bed has been worked out
under the gravel.

Eastward, where the ground sinks towards Coldham Common, numerous
pits have from time to time been opened, and the coprolite bed under this area
is now nearly exhausted. It is only necessary to describe one or two of the
sections here shown ; the following was seen in a pit on the west side of the
cart-road about a quarter of a mile N.E. of Polecat Farm :— •

Feet.

Greyish- white marl - - - - - 10

Greenish-grey, intermixed with greyish-blue clunch,

the beds of the latter being chiefly in the lower part,

both hard and lumpy - - - - 9

Dark sandy marl, with coprolites - - about 1

Another pit near the brook to the S.E. showed an inclined surface of Gault,
the clunch being 20 feet deep at the N. end and only 15 feet at the other, the
upper 6 feet of the marl were soft and clayey, becoming rather harder and
more lumpy below, the next 8 or 10 feet presented a rough face, consisting of
lumps of hard bluish-grey clunch set in a loose clayey matrix ; there were
many cracks and open interstices stained with iron or manganese. Below the
rock became more nomogeneous, and passed down into hara marly greensand
with coprolites, breaking into lumps ; underlying this was a bed of very dark
clayey marl, and then the usual seam of dark clayey greensand with nodules,
resting on the Gault. The foreman, Henry Coe, stated that the nodule bed
was frequently double, as above described, and that the intervening seam was
often a dark clay resembling Gault ; when double, the thickness to the top of
the upper bed would be about 18 inches.

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QHALK MABL. 33

Under Coldham's Common the coprolites have been worked at varying
depths, down to 24 feet near the brook. We have abready mentioned (p. 18)
that they have been taken out from under the marl in the brickyards at Bam-
wellj and that they run up here to a much higher level than their horizon
under the Common. This rise, indeed, brings the Gault to the surface in the
hollow 'between the railway and the brook, but the marl passes down again
below the alluvium north of the bridge by the old paper mill.

In 1876 the northern slope of this Gault ridge was visible in a pit on the
east side of the brook, and south of the Newmarket Road ; at the back of the
garden-wall the Gault lay at a depth of 25 feet, and thence its surface sloped
rapidly up in a S.S.E. direction ,the nodule bed cropping out near the bottom of
the same field, but in the S.E. corner of this shallow pockets with nodules
were found. The foreman estimated the length of the trench at about 200
feet, so that the apparent inclination of the surface was about 7^> but he
believed the deepest slope to be towards the N.£. or N.N.E. The slope was
fairly even and regular, and the thickness of the Greensand seam was greatest
in the deeper part of the pit ; but the portion of this containing the coprolites
did not seem to vary, but kept much the same thickness throughout. The
section here was similar to that represented in Fig. 6.

South of the farm to the east there were workings in 1874-6, about 10 or
12 feet deep, these must have been on the southern side of the ridge, which
appears to be continuous for some distance. It was again proved at pits about
a quarter of a mile south of the old turnpike at the corner of the road to Ditton ;
the trench here completely intersected it from N.N.E, to S.S.W., and showed
the nodule-bed dipping down a slope of Gault in each direction, the top of
the ridge being between 7 or 8 feet of the surface of the ground.

From the top of the ridge above described the surface of the Gault, and with
it of course tne Cambridge Greensand, slopes northward till it is found at
a depth of 33 feet under Fen Ditton. A quarter of a mile S.W. of the church,
and near the level of the alluvium, it was touched at a depth of 16 feet, it
would appear therefore to pass under the alluvium and the river-bed, it
certainly reappears on the western bank, and has been worked under the fields
by Ditton corner. Workings also have recently been opened (1878) on the
alluvial level N. of the Plough Inn at Ditton.

About Homingsey there are extensive excavations, but nothing of special
interest was seen in the trenches. We were informed by Mr. Fyson, of
Homingsey, that his father was one of the first to dig and wash the coprolites
soon after the discovery of their conunercial value by Professor Hbnslow;
many thousand tons have been raised from, this parish.

Between High Hall and Herdwalk Common there is a Gault inlier forming
a considerable area of dead ground, being about 600 yards long and nearly
200 wide at the south end. A trench opened in 1876 showed the greensand
cropping out and dipping eastwards beneath 6 or 6 feet of fine sandy
gravel, which became tninner as the nodule bed sank under the Marl towards
the Fens.

Fig. 3. Section across the Fields about Haifa Mile N'.W. of
Homingsey*

Scale 8 miles to an inch.

a. Gravel. h. Chalk Marl. c. Gault.

At the east end of the trench the section shown was this : —

Feet.

Black fenny soil - • * - 1

Gravel and sand in pockets - - - 3

Greyish white clunch - - - - 6

Sandy vein with cops • - - - J

Northward of this many irregularities and ridges were to be seen in the

surfieice of the Gault when disclosed by the workings for coprolites. (See

Qmri* Journ, Geol, Soc, xzxi. p. 260.)

N309. O

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34 Gr.OLOGY OP THE NEIGHBOUBHOOD OP CAMBRIDGE.

A small outlying patch was worked close to the lane leading northward
from Clay Hythe, in a hollow, the maximum depth of which wm 7 or 8 feet ;
an irregular ridge of Gault separated this from the deeper excavations to the
eastward, where the nodule bed sloped gradually down towards Bottisham
Fen. Under this Fen the bed has been proved in many places to the
S.W. of the Bottisham Lode, so that its outcrop could be entered on the map
with considerable accuracy; the extreme irregularity of this line indicates
how uneven is the sur&ce on which it rests, and a further demonstration is
afforded by the fiict that instead of continuing its normal dij) towards the
S.E., the surface of the GaiUt actually rises in this direction, and is exposed as
a long narrow strip between the fen-edge and the outcrop of the Chalk Marl
near the village called Bottisham Load. This feature produces the curious
phenomenon of an outlier existing at a lower level than that occupied by the
outcrop of the main mass ; this small patch lies under the fen nearly a mile
N.E. of Long-Meadow Farm. Three quarters of a mile north of this larm the
outcrop again passes under the fen and crosses the Swaffham Load.

llie phosphates have been extracted from underneath a large portion of
Swaffham Fen, but many pits were open in 1875-6, with depths varying from
3 to 15 feet. The section exposed in one of them at the corner of the roads,
named respectively ** White " and " Black '* Droveways, is given below :—

Feet.
Black peaty soil - - - - 1

Fine yellow silty sand - - - - 4

Clunch, with coprolites at the base - - 7

The greensand thrown out had very little admixture of clay, and dried into
laminated greenish white lumps. Similar sections were to be seen in the pits
southward and northward, and the phosphate nodules extracted from all of
them exhibited different characters to those obtained nearer Cambridge. There
was a much greater proportion of light-coloured phosphates, and the fossils
which occurred amongst these had not apparently been subjected to much
rolling, but retained their shells in a more perfect state than usual, TerebratuUs,
Rhynchonelke, and Exogyra being especially common and well preserved;
RadioUtes Moretoni and Pharetrospongia Strahard from the Marl itself are also
abundant in this neighbourhood.

Amongst the darker nodules there are some which have a greenish exterior,
and the whole assemblage has a different aspect from those to the south, as if
resulting from the erosion of differently constituted beds in the Gault.

In connexion with the peculiarities presented by these nodules
it may be mentioned that one of ns, when accompanying Professoi
BoNNEY some years ago, saw an excavation near Reach, where
a second coprolite bed was worked in the mass of the Gault about
8 feet below that forming the base of the Chalk Marl ; the washed
heap of nodules contained fossils from both seams, but the species
were all the same as those usually found in the Cambridge bed.

It is probable, therefore, that the erosion of local seams of nodules
in the Gault contributed to the accumulation of the various kinds
of nodules and fossils found at the base of the Chalk Marl.

From Reach the marl has been followed under the Fen, west of
Burwell, towards Wicken, but this locality is not within the area
described in this memoir.

The great number of outliers which occur to the westward of
the main line of outcrop is-reraarkable, but the two circumstances
which have contributed to their formation are not far to seek ; the
one is the fact we have had occasion to point out so frequently, the
uneven surface of the Gault, for the hollows filled with Chalk Marl
are of co^irse left as outliers when the rest of the chalk has been
removed ; this will account for the number of small patches scattered

Digitized by VjOOQ IC

CHALK MABL. 35

over the Gault area, from which the coprolites have been worked
out under a varying thickness of Chalk Marl. The larger outliers
owe their existence to the tongue-like projections of Boulder Clay,
which, stretching eastwards from the main mass of the clay, have
protected those portions of the Chalk which underlie them ; the
ridges previously mentioned (page 16) have thus been produced.

The first outlier in the S.W. corner of Sheet 51 occurs between Wendy and
Whaddon ; it occupies a long hollow or channel in the Gault^ for though about
three-quarters of a mile in length from S.W. to N.E.^ it makes no feature
whatever on the ground ; its maximum depth in the centre was about 12 feet,
but the surface of the Gault was s6en to be very irregular, and in one part
between it and the Chalk was a small layer of ferruginous sand.

The next outlier occurs on the slope N.W. of King's Bridge, and must be
some 30 feet above that spot where the nodule bed was S)und below the
alluvial level of the river Bliee. Other outlying patches occur to the N.E.,
between Orwell and Barrington.

To the northward lies the long ridge which rises into the Orwell and Has-
lingfield hiUs ; the coprolite bed has been followed all round these, and has
been or is being extracted from all places where it lies within 20 feet of the
surfiEu;e. At Harston it has been dug close down to the river bed ; this occurred,
for instance, about half a mile S.S.W. of the church and it may possibly
extend under the river here in a narrow neck so as to join on to the main mass
about Hoffer Bridge.

The greater part of Barrington stands upon Gault, which rises up to form
an irregular ridge hereabouts, but the church is built on a small outlier of
Chalk Marl, and in 1875 the pits to the westward exposed the northern edge
of the Gault ridge, which was seen " sticking up hke a wall " along these
workings, the fossil bed following it, and in places standing almost vertical.
The foreman says that on the back or hill-side of these ridges, where they
occur, is often found a second seam of fossils, separated from the lowermost
by a foot or so of marl or marly clay.

At another pit, three-quarters of a mile west of the church, they were work-
ing on the slope of a Gault ridge that pitched down at an angle of 30 or
40 degrees ; according to the workmen this rolled over to the north where
they had worked out the coprolites, and the layer containing these cropped out
on each side ; the Gault here was also full of slickensided surfaces.

One of the Coprolite pits on the south side of road, near Foxhole Down Farm,
Orwell, showed a gradually increasing slope of Gault slightly undulating in
the deeper parts, and broken into numerous irregular and steep-sided pockets
where it rose within 2 feet of the surface.

This pocketty condition of the outcrop is very frequent where the seam rises
at a low angle^ and coprolites are always dug out of the holes ; it does not seem
to be in any way connected with the erosion of the Gault, but it is difficult to
account for the phenomenon in a satisfactory manner. Mr.O.FisHER has figured
an instance of tnis which he kindly allows us to reproduce, he attributes the
hollows to the agency of ice, and without endorsing this opinion we admit that
pressure of some kind seems to have come into action, for when the clay forming
the sides and bottom of the pockets is lifted up with a spade it exhibits a platy
structure with striated surfaces, greatly resembling slickensides.

Fig. 4. — Section in a Coprolite Pity east of Harlion,

(For the use of this Fig. and Fig. 5, we are indebted to the kindness of the author

and of the editor of the Geological Magazine,')

Scale, 12 feet to an inch.

a. 6. Soil and gravelly earth. (*• Warp and Trail " of Mr. Osmond Fisher).

c. Pockets of phosphate nodules, 1-2 feet deep. d, Gault.

c 2

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36 GEOLOGY OF THE NEIGHBOURHOOD OP CAMBRIDGE,

The coprolites have recently been dug all along the outcrop north of Wim-
pole ; the surface of the Gault was seen to be often irregular, and the nature
of the Greensand very argillaceous. A marked ridge of Gault runs up the small
valley west of " Wimpole Ruins '' at right angles to the direction of the ridge
along the valley from " Wimpole Hole."

Pits near the latter place exhibited the following succession of beds : —

Feet.
Boulder Clay- - - - - - - 2

Grey Marl, with occasional lumps of hard dunch - - 4

Hard blocky clunch (with Marl between the lumps) - - 6

Coprohte bed - - - • - - -i

The outcrop of the Marl in this neighbourhood is regulated by that of the
outlying Boulder Clay, the presence of which has preserved it from denudation.

To the S.E. of Wimpole are two small outUers, one of the Marl and Coprohte
bed ; the other mere traces only of the latter, with Coprohtes scattered on the
surface.

Crossing the ridge to the northward the irregular outcrop of the Marl about
Eversden may be noted.

At Harlton two marked indentations of the line will also be seeo, one of
these is caused by a ridge of Gault which was found running southwards
through the field adjoining the Rectory garden.

Between Harlton and Haslingfield Mr. O. Fisher noticed several curious
sections in the Coprohte pits open in 1871.* Fig. 6 is one of these, and shows
a small slip or fault affecting the nodule bed, such slips are not uncommon ;
for a description of the other section, which is more complicated, we must refer
the reader to the paper in the Geological Magazine,

. Fig. 5, — Section in a Coprolite Pit between Harlton and Haslingfield,

Scale, 4 feet to an inch.

a, h. Soil and grave]
c. Chalk Marl.

' earth (Warp and Trsdl of Mr. Fisher).
d. Nodule bed. e, Gault.

At Haslingfield the church and the greater part of the village stands upon
Chalk Marl, but a strip of Gault runs through the north end of the village,
separating the mass of chalk on the south side from an outlier of considerable
size, which occupies the ground to the northward, and from which the phosphate
nodules have now been almost entirely extracted.

The outcrop of this outher makes a well defined rise in the road leading to
Cantalupe Farm, and barelv a i mile north of this point on the left side of
the road there was a trench aug for coprohtes in 1875, which was about 30
yards long, and had a depth of 20 feet at one end; the nodules were embedded
m a yery dark clayey marl, containing fewer glauconite grains than usual, and
the seam was inclined at an angle of about 1^, rising up along the surfrkce of
the Gault till it cropped out under the soil.

* Geol. Mag. vol. viii. p.^68-70.

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CHALK MABL.

Fig, 6. — 'Section in a Coprolite Pit N.E, of Haslingjield,

a. Soil.

Scale, about 40 feet to an inch.
b. Chalk Marl. c. Nodule bed. d. Gault.

The result of this dip was to produce a long patch of " dead ground "
extending across several fields to the west for the distance of half a mile ; the
average breadth of this was about 100 yards, and beyond this strip of clay the
Greensand seam again came on and dipped northwards, but did not descend to
such a depth as on the south side, the trenches dug to work it being only about
8 or 10 feet deep. Further north it appeared to rise again slightly, and ap-
proaching the surface extended over several acres of ground in a remarkably
pocketty condition, the nodules being dug out of holes like those sho^vn in
Fig. 4.

In a field about a quarter of a mile S.E. of the above-mentioned section two
other patches of " dead ground *' were found to exist ; at the time of our visit
a trench was dug across the intervening hollow in a direction about N.E. by N.,
at the southern end of this the nodule bed cropped out under 3 feet of clayey
soil, but sloping down rapidly northward it soon attained a depth of 22 feet,
rising again irregularly it reached the surface at a distance of about 120 yards
from the former outcrop. The Greensand seam was thickest in the deeper
part of the hollow, the oark Glauconite Marl extending upwards fuUy 2 feet
above the surface of the Gault, and the phosphate nodules being there accumu-
lated to a depth of about 12 inches, while near the outcrop there were hardly
any nodules in the Marl.

The following diagram shows the general relations of the Gault and Chalk
Marl at this place, and explains the manner in which the spots of "dead
ground " have been produced.

JFtff. 7. — Diagram Section across the Field N.E. of Hasling^eld.

i b

Scale, horizontal and vertical, 300 feet to an inch.

The broken line shows the former continuation of the Coprolite bed.

a. Chalk Marl. b, Gault,

On the slope to the south the marl and coprolites occurred again in a shallow
channel on the flank of the hill, which was not deeper than 5 or 6 feet, and
the intervening ridge of Gault seemed to widen out towards the river, but it
was not possible to find out the exact lie of the beds here, as such details can
only be ascertained when the ground has been trenched for working the copro-
lites. Northwards, towards Cantalupe Farm, the depth of the works averaged
about 20 feet. ^

In the neighbourhood of Grantchester there are two long outliers resting on
the flanks of a Gault ridge, which comes to the surface along the higher
ground between Grantchester and Barton, crossing the main roaa by the third
milestone from Cambridge, as shown in Fig. 9. Just north of this point the
nodule bed was seen cropping out under 4 feet of loamy soil, and dipping down
to the north at an angle of 20°, for at about the distance of a chain it lay at
the depth of 26 feet.

The outlier, of which this forms a part, stretches eastward to the river bank
north of Grantchester, westward it is cut off from the mass underlying Barton
Field by a narrow neck of Gault, and its northern boundary lies at a much

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38 GEOLOGY or THE NEIGHBOURHOOD OF CAMBRIDGE.

lower level than the Bouthern, where it rests against the Gault ridge previouBiy
mentioned.

Fig. 8. — Section through GrantcJiester.

CpBS

Horizontal scale, 3 inches to a mile ; vertical scale, 200 feet to an inch.
a. Gravel. h. Chalk Marl. c. Ganlt.

In 1874-75 another small outlier of marl and coprolites was worked on the
north side of FuU Brook ; these lay in a hollow, which was 20 feet deep in
the centre near the road, but the surface of the Gault rose up rapidly towards
the brook, forming a bank against which the Chalk Marl was bedded ; the
nodule seam appeared to thin out on approaching this, and passed into a few
inches of sandy marl on the steep slope. The workmen stated that the seam
averaged 9 to 12 inclies in the hollows and not more than 6 inches on the
ridges, and that sometimes it was absent altogether.

The nodule-bfed has been worked all round the edge of the Marl bordering
the Boulder Clay over Barton and Coton Fields, and a shallow outlying patch
about three-quarters of a mile east of Coton was dug in 1873. The surface of
the Gault here exposed was extremely uneven, and the Greensand was followed
in and out of the various hollows^ so that its boundary can only be shown by
a very general line on the map.

In 1876 there were workings west of Whitwell Farm, which passed through
a few feet of Boulder Clay before reaching Chalk Marl, and there must be a
considerable area of the marl concealed by this clay to the northward and
westward.

The Coton ridge was doubtless at one time continuous with that which
runs from the Observatory to Castle Hill, from under which the coproUtes
have been dug out at a maximum depth of 24 feet ; near the gaol they must be
covered by about 30 feet of Chalk Marl, but the underlying Gault rises up
to the northward and forms a ridge running through the Cemetery and across
the road to Histon. Beyond this is another small outlier, from which coprolites
have been obtained between the windmill and the hsm to the N.E. ; but the
portion adjoining the road has not yet been worked so far as we can ascertain.

By the windmill, half a mile N. W. of Chesterton, a small patch of Chalk
Marl occurs, from which the coprolites have been extracted, and extends from
the top of the clay pits to the back of Rose Cottage, where it underlies the
gravel.

To the north of Chesterton two other small outliers were found beneath the
gravel, and the coprolites were all extracted from them in 1873.

In the preceding pages the uneven surface on which the Green-
sand rests has been the subject of frequent remark, and we have
seen that the irregularities sometimes present the appearance of
long undulations, and sometimes of local irregular ridges and
hollows. Hitherto we have referred these inequalities to a single
mode of origin, the action of current erosion ; but it is at any rate
possible that another cause may have co-operated in their pro-
duction ; the existence of small anticlinal and synclinal flexures,
aflfecting both Gault and Chalk Marl alike, would give origin to
similar appearances. It is accordingly desirable that we should
inquire how far this latter cause may have assisted in producing
the present aspect of the uneven surface.

Such small flexures have been observed to afiect the higher parts
of the Chakl, but they may or mav not extend downward so as to

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CHALK MARL. 39

affect its base also : the probability is, indeed, that some of them
do ; it will, for instance, be shown in the sequel that a shallow
synclinal strikes through the Gog- Magog Hills from S.E. to N.W.,
and it is probable, therefore, that the depression of Coldham
Common is only the continuation of this synclinal trough. It is
also a fact that in this vicinity little difference was observed in the
thickness of the nodule bed, while in those hollows which are
clearly the result of erosion there is generally a greater accumula-
tion of nodules ; but the clay ridge near t he Newmarket road had
more the appearance of a '' hogsback " or bank left by erosion.

We cannot, however, point to any other instance of a roll or ridge
to which this hypothesis appears applicable. It might be thought
that the low ridge running through Grantchester was a similar case ;
but its direction is nearly due E. and W., while that of all the
folds observed in the Chalk is from S.E. to N.W. ; again the Grant-
chester ridge is prolonged into an irregular hummock of Gault near
Barton, the greatest width of which is from north to south. The
surface here has evidently been modified by local erosion ; con-
sequently it must remain doubtful whether subsequent flexure has
had anything to do with the formation of the ridge.

As regards the minor hollows and ridges so frequent in the S.W.
portion of the area described, near Whaddon, Orwell, &c., there
can be little doubt that they are the result of current erosion, as
originally suggested ; all the phenomena connected with them are
only explicable on this supposition, and the mere fact that they
exhibit no constancy whatever in the direction of their greater
length is sufficient to negative the idea of their being in any way
due to lines pf flexure.

It is equally impossible to attribute the remarkably uneven
surface of the Gault near Horningsey to any arrangement of anti-
clinals and synclinals. The greater depression appears to have
its longer extension in a S.W. and N.E. direction, while the minor
ridges are quite irregular, some being transverse to this, and others
running nearly N. and S.

We conclude, therefore, that of the two causes assigned for the
production of these inequalities in the surface of the Gault, that of
subsequent flexure is seldom applicable, and that by far the greater
proportion of cases are due to local erosion during the deposition
of the Greensand itself.

Chalk Marl.
Zovie of Rhynchonella Martini,

The beds composing the mass of the Chalk Marl vary somewhat
in colour and texture, but are always more or less argillaceous.
The few feet immediately overlying the nodule bed consist of a grey
clayey marl, with a sprinkling of glauconite grains, which diminish
in number upwards. The next 10 or 12 feet Jire often harder and
more lumpy, sometimes bluish and sometimes greenish-grey ; these

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40 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

pass into softer greyish-white marl or elunch, above which are
about 40 feet of similar grey or bluish argillaceous rock. The
whole thickness is about 60 feet at Cherry Hinton near the line of
section in the Plate^ and it seems to preserve the same average
thickness across the area shown in the map (Frontispiece), though
it may thicken somewhat to the S.W.

The lower part of this Chalk Marl is well exhibited in the
numerous coprolite pits, which are frequently between ^0 and 30
feet deep ; but the upper beds are not often exposed.

In describing the sections the same arrangement will be adopted
as with those of the coprolite bed.

Main Mass.

The outcrop of the Chalk Marl enters Sheet 47 near Bassing-
bourn, and stretches to the N.E. between the boundary lines of
the Cambridge Greensand and the Totternhoe Stone by Whaddon,
Meldreth, and Shepreth. From hence to Cambridge its surface is
much obscured by outspreads of river gravel. Eastward from
Cambridge the Chalk Marl occupies a considerable area, Tever-
sham, Ditton, Horningsey, Quy-cum-Stow, and Wilbraham Fen,
Bottisham, Swafiham Bulbeck, and Long Meadow being all situate
upon this lowermost zone of the Chalk. The more prominent
portions of the ground, as those near Teversham and Bottisham,
may be capped by small outliers of Totternhoe Stone, but in the
absence of sections it is impossible to be certain of their existence.

The first exposure noted by us is the small clunch pit marked on the
Ordnance map east of Shepreth; in this the nodular basejof the Totternhoe
Stone is shown with a few feet of the underlying Chalk Marl. There is
nothing which can be called bedding in the latter, but it is curiously jointed,
the lines of separation presenting in one place a concentric appearance. The
material is rather tough than hard, and breaks with a curving marly fracture.

In the clunch pit on the north side of Hauxton Mill Bridge there is 12 or
15 feet of soft crumbling grey marl containing a few small Brachiopods and
fragments of Inoceramus ; the bottom of this pit is probably not more than
20 feet above the nodule bed, so that this is at a lower horizon than that at
Shepreth.

The lowermost beds of the Chalk Marl, as seen in the coprolite pits at
Trumpington, Coldham Common, and elsewhere, have already been described
(see pp. 32, 36).

At the waterworks, on the road from Cambridge to Cherry Hinton, the
large receiving well was originally dug down to a depth of 46 feet, and the
beds passed through were as follows (see also p. 159) :—

Feet.
Soil and light-coloured clay - - - - 6

Dark clunch - - - - - - 23

Light-coloured clunch - - - - - 7

Grey chalk - - - - - - 4

Blue "gaulf* (clunch) 6

The nodule bed of the " Cambridge Greensand " was found below, when the
well was deepened in 1875, the surface of the true Gault being 48 feet from the
top, so that the above is almost a complete vertical section through the Chalk
Marl, for the thickness of the clunch between this spot and the outcrop of the
Totternhoe Stone cannot be more than 10 or 12 feet. Bluish shaJy marl is
thrown out of the ditch between the waterworks and the well-head, which may
belong to that termed ** dark clunch '* above.

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CHALK MARL. 41

A well near the cross-roads at Fen Ditton was sunk through 33 feet of
Chalk Marl, and a strong spring was found in the nodule-bed at its base.

The softer and more clayey portions of the marl are sometimes dug and
shaped into large bricks, which are dried in the Sun and used in the construc-
tion of outhouses and other rough buildings; shallow pits whence such
material has been obtained occur, by the roadside half a mile south of Anglesey
Abbey, and near the hamlet called Long-Meadow, west of SwafPham Bulbeck.

North of the last-mentioned village the greater part of the Chalk Marl is
hidden under the black soil of Swaffham Fen, but its lower beds are shown in
the coprolite pits, and its uppermost layers are found in the clunch pit two
furlongs S.S.E. of Swaffham Abbey.

Its upper portion is again seen emerging from under the '^brassel^'* or
Tottemhoe Stone at the west comer of the large quarries near Reach (see p. 48),
and the thickness exposed along the south-western face is about 30 feet ; the
mass of this is a greyish-white blocky clunch, rather hard when dry and break-
ing with a marly fracture ; the bedding is indistinct, but the joints are strong
and numerous ; this clunch passes down into darker and softer br6wnish-grey
marl and finally into bluish shaly marl, of which 3 or 4 feet are shown at the
bottom of the quarry, these lower beds being full of fossils. At the cottages
north of the quarries the wells are between 20 and 30 feet deep, so that the
thickness of the Chalk Marl here must be about the same as at Cherry Hinton,
or from 50 to 60 feet.

Similar firm Chalk Marl is to be seen underlying the Totternhoe Stone in
the northern pit at Burwell (see p. 47).

Outliers.

There are only two outliers which contain any great mass of Chalk Marl ;
that between the valleys of the Rhee and Bourn, and that underlying the hills
between Madingley and Barton ; the former comprises the whole of the zone and
much even of the overlying Grey Chalk intervenes between it and the capping
of Boulder Clay ; the latter too along its southern slopes in Barton Field must
display almost the entire thickness of the Marl, but northward the base line of
the Boulder Clay gradually descends and cuts out its upper beds, leaving little
more than half its thickness under Coton Hill.

Most of the smaller outlying patches of the Chalk Marl have already
been mentioned in describing the noduliferous layer which lies at their base.
Good sections of the beds overlying this were seen in some of the coprolite
pits and are noticed at pp. 32, 36 ; as however, the nodules have now been worked
out from underneath nearly all these outliers, future excavations in them will
only disclose the disturbed and broken-up materials which were thrown back
into the trenches.

In the clunch pit three-quarters of a mile south-east of Kingston the
following beds are seen : —

Feet.
Rubbly chalk - - - - 5

Grey sandy chalk - - - - 1 i

Rubbly chalk - - - - 3

Grey sandy chalk - - - - H

Hard blocky chalk or clunch, about - 10

The nodule bed lies below this, but is not seen on account of the talus ; a
tunnel was commenced here for working the coprolites, but so much water was
met with that the undertaking was abandoned.

Another pit, half a mile W.S.W. of Harlton, shows about 20 feet of greyish
marl or clunch, containing small Brachiopods and other fossils. The base of
this must be 20 or 25 feet above the coprolite bed.

A clunch pit, south-eastward of Madingley, is cut through Boulder Clny to
Chalk Marl, about 20 feet of the latter being shown with an irregular hard
bed 2 or 3 feet thick near the top.

* We cannot answer for the spelling of this local terra, ? allied to " brash, or to
6ros«i7," a name given to layers of hard rock in the Midland Counties.

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QEOLOGT or THE NEIGHBOURHOOD OP CAMBRIDGE.

List of Fossils from the Chalk Mabl.

:::

...

• ••

X
X

••

X
X

...

X
X

...

Lamna (tooth)

Otodus appendiculatU8, Ag. -

Ammonites varians, Sbt/, -

Inoceramus latus, var. Reachensis,

Ether,
lima globosa, Sby, - - -

Ostrea vesicularis, Lam.
Pecten orbicularis, Sby.
Plicatala inflata^ Sby.

Kingena lima, Defr.
Rhynchonella grasiana, D^Orb,

„ Mantelliana, Sby. -

„ Martini, Mant

Terebratula semiglobosa, Sby,

„ biplicata, Sby. -

Terebratulina gracilis, Sby. var.
uodulosa, Ether,
„ striata, Wahl. -

„ var. triangularis, Ether,

Cidaris dissimilis ? (spines) -
Discoidea subucula, Klein -
Holaster subglobcsus ? Leske

Serpula annulata, Retiss
Verraicularia umbonata, Sby.

X ?

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LOWER CHALK. 43

CHAPTER V.—LOWER CHALK.— continrnd.

Grey Chalk.
The ToUemhoe Stone.

Above the Chalk Marl, and generally forming the first rise in
the escarpment of the Lower Chalk, there occurs a compact sandy
chalk, which appears to be the representative of the well-known
Totternhoe Stone. Like that rock it consists of a light greyish
brown or buflF sandy chalk, containing many organic remains and
small scattered brownish phosphate nodules. Being a sandy and per-
meable bed, and resting as it does upon argillaceous mafls below,
it is naturally a water-bearing bed, and its outcrop may indeed be
roughly traced by means of the strong springs thrown out at
intervals from its base.

Mr. Whitaker has described the Totternhoe Stone in its course
through Bucks, Beds, and Herts, and has traced it north-eastwards
as far as Hitchin ; he also observed it near Ashwell,* and from this
locality we have traced it through Cambridgeshire as far as
Burwell.

The stone has been largely quarried in many places for building
material, and has been used in the construction of many of the old
churches in Cambridgeshire ; being easily cut and carved it serves
excellently for interior mouldings, but unless the blocks are care-
fully chosen it is liable to weather and crumble away when used
for exterior work.

Analysis of a Specimen of Totternhoe Stone from Burwell, by
Dr. Frankland.

Composition in 100 parts.

Moisture^ at 100 degrees - - - '66

Alumina ----- -53

Sesquioxide of iron (partly protoxide) - '68

Ciddc carbonate - - - - 85'91

Mag^esic carbonate, trace . . -

87.78

Insoluble Residue (Clay).
Silica 8-5

{'32
1*19
Lime - - - - - '28

Magnesia ----- '29

Organic matter •^ • - - *44

Main Mass,

11-02
98-80

The most easterly point where Mr. Whitaker has recorded tlie occurrence
of Totternhoe Stone is at the spring-head of the river Rhee, east of Ashwell
Church.t A similar spring-head, half a mile S.S.W. of Bassinghourn
Church^ in Sheet 47, is doubtiess an indication of the same stone overlying the

* Geological Survey Memoirs, vol. iv. pp. 38-42 (1872).
t Ibid. p. 42.

X On the Ordnance map the watercourse is continued too for westward, the spring
is at the point where it takes a sharp turn to the north.

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44 aEOLOGY OF TUB NEIGHBOUEHOOD OF CAMBEIDGE.

Chalk Marl. From Bassingboum it probably runs through Kneesworth along
the edge of the rising ground south of Dyers Green. In 1816 Prof. Hail-
stone, speaking of the Burwell Stone^ remarked '* that in an extensive pit at
Kneesworth, on the other side of the county, the same bed occurs again, where
it preserves an uniform thickness and direction." Trans. GeoL Soc, vol. iii.,
p. 249. A pit by the roadside, about three-quarters of a mile west of Mel-
bourn Station, shows some 2 feet of lumpy clunch like that noted in many
coprolite pits, but also seen elsewhere about the horizon of the Totternhoe Stone.
Hard chidk occurs in the railway cutting N.E. of Melboum Station^ and
may represent the Totternhoe Stone, but no good exposure of it is seen any-
where in this district.

The Totternhoe Stone probably enters Sheet 61 by the Old Paper Mills
S.E. of Shepreth, and its basement beds are exposed in the clunch pit pre-
viously mentioned near that villajje (p. 40) ; above the Chalk Marl there is
a layer of greenish nodules, similar to that which forms the base of the stone
at Reach. Many of these nodules are covered with Ostrea 'vesicularis, and the
following fossils were also found in and above this band, — Holaster subglobosus,
Plicatula inflata, Terebratula, and Ostrea normaniana ?

From this point the line is simply drawn to follow the natural features of the
country, imtU it enters the railway cutting near Harston, where a hard Grey
Chalk was passed through ; the rock may be seen in the clunch pit S.W. of
the station, and greatly resembles Totternhoe Stone » being hard, grey, sandy,
and fossiliferous. From Harston the line is carried by contour to the " Well
Head," south of Hauxton, which is doubtless'thrown out at the base of this
division ; thence the line turns eastward and passes under the gravels of the
Cam Valley.

The Totternhoe Stone must underlie Shelford, and it doubtless gives rise to
the springs called the Nine Wells, three-quarters of a mile north of the j*ailway
junction, the hollow N.E. of this was once a marshy pool or mere, and the soil
turned up by the plough is full of freshwater shells.

The feature made by the Totternhoe Stone may be traced across the fields
beyond the Red-cross Toll-gate, and there are springs by the cottages north of
Nether Hall.

In the large quarries near Cherry Hinton, just to the east of the line of
section, the top of the Totternhoe Stone is touched and some depth of it was at
one time worked for building-stone, now however not more than A^or 5 feet can
be seen at the bottom of the quarry ; the stone passes upward into the whiter
chalk above, but lower down it becomes darker and more sandy, according to
the workmen. A well near the cottage is sunk to a depth of 20 feet, the water
level being about 10 feet below the present bottom of the quarry, and as the
springs are thrown out at the junction of the Totternhoe Stone with the
Chalk Marl, this would give about 15 feet for the thickness of the former at
Cherry Hinton.

The base of the Totternhoe Stone appears to be exposed in the railway cut-
ting north of Fulbourn Asylum, 6 or 6 feet of blocky clunch being overlaia by a
similar thickness of hard grey sandy stone, with a nodular bed at its base ; at
the east end the beds seem to be faulted downwards a few feet. The top of the
stone is shown in the small clunch pit to the south of the line, forming a soUd
bed of grey sandy rock about 3 feet thick, and containing RhynchonelU,
Mantellianay Terebratula semiglobosa, Avicula grypjueoides, and Vermiadaria
umhonata. The spring supplying the parish pump, called the Poor Well, at
the western end of Fulbourn, is probably from the Totternhoe Stone. The
connexion of this spring with the water level under the hills is shown by the
fact that when it was dammed up in order to clear out the well, the water rose
in the well at the Windmill on the hill to the S.W., and sank down again
when the Poor Well was re-opened.

The boundary of the Totternhoe Stone then turns northward round the low
hill which projects into Fulbourn Fen. The railway cutting shows about 12
feet of grey lumpy clunch, with pockets of hard yellow marl and gravel, this
must be just above or in the top of the Totternhoe Stone, which seems in some
places to put on a nodular character ; the wells in the road near the railway
station are about 10 to 12 feet deep, and their sides exhibit the nodular lumps
of chalk, which are popularly called " chalk-stones ; " the water used to over-

Digitized by VjOOQ IC

LOWEE CHALK. 45

flow firom these wells in the winter before Willbraham Fen had been drained
to its present level.

At the springs called Shardelow's Well, E. of Fulbourn, the water bubbles
up very freely, and forms the main supply of the Wilbraham River, the other
branch coming from sources to the N.E. of Great Wilbraham. AU these
springs are probably from the base of the Totternhoe Stone, but it is impossible
to trace the outcrop of this zone under the superficial deposits in this neigh-
bourhood ; it is most probable, however, that it runs out for some distance to
the N.W. of Wilbraham, under the ridge of gravel which stretches in that
direction, and that the line turns back along the opposite slope to Spring Hall,
near Bottisham, The spring here is probably thrown out at the base of the
Totternhoe Stone, and thence the boundary line turns northward to the
Whiteland springs, which are doubtless on the same horizon.

From this point a low ridge or scarp may be traced north-eastward through
Swaffham Bulbeck and Swaffham Prior, forming the first rise from the Chalk
Marl plain to the hilly country on the east. At the same time signs of dis-
turbances or undulations in the level of the beds begin to appear ; the out-
crop of the Totternhoe Stone does not altogether correspond with this ridge,
and in the pits near the windmill east of Swafi^am Bulbeck the beds are seen to
dip into the hill on each side ; in the small clunch pit between the Swaffhams,
where one would expect the Totternhoe Stone to be exposed, nothing like it is
seen, and the beds shown appear §> belong to the underlying Chalk Marl.

N.W. of this, and just before entering Swaffliam Prior, the road traverses a
curious hollow or combe, a strong spring used to issue from this, but the source
was enclosed in 1870, and the watercourse through Mr. AUex's grounds has
been dammed up to make a pond and rockery. It is probable that a slight
synclinal in the Chalk is the cause of the abundant water-supply at this point,
and the same appears to be the case at Cherry Hinton (see p. 130).

At the bottom of the clunch pit, a quarter mile N.E. of Swaffham Prior
Church, there is a hard grey sandy stone exposed which much resembles
Totternhoe Stone, containing small brown phosphate nodules and some fossils,
such. M Rhynchonella MantellianOy R.grasiana, Terehratula semiglohosa, Kingena
lima, and Vermicularia umhonata. The level of this bed is considerably above
that of the spring above mentioned, and if it belongs to the upper part of the
Totternhoe Stone this must be brought up by a rise in the beds or by a fault.

To the northward there is a disturbance which affects the boundary lines
considerably, for there appear to be two anticlinal axes rimning from S.S.E.
to N.N.W. and bringing up the Chalk Marl on each side of Burwell as shown
in the section Fig. 9.

.Fi(/, 9. — Diagram-section through Beach and BurwelL
W.8.W ' E.N.E.

Boad. Devil's Dyke. Stream. Road. Mill.

i II

Horizontal scale, 2 miles to an inch. Vertical scale, 200 feet to an inch,
o. Totternhoe Stone. h. Chalk MarL

Under these circumstances it is difficult to trace the outcrop of the Totternhoe
Stone with any accuracy between Swaffham Prior and Burwell. The southern
portion of the latter is built upon a projecting tongue of the stone which
appears to lie on the slope of a synclinal hollow. The stone crops out near the
road leading S.E. from the High Town Windmill, and probably also at the
base of the bank running north and south on the western side of the main street.
Excellent sections are to be found in the numerous quarries to the east of
this street*

Perhaps the best exposure of Totternhoe Stone is seen in that called Carter's

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46 GEOLOGY OF THB NEIGHBOUBHOOD OF GAHBBIDGE.

pit near the church, and where this has been recently worked near the stable
the section is as follows : —

Feet.

Soil and chalk rubble - - - - 4

Thin bedded greyish white chalk - - - 10

r Course of hard brownish-grey stone project-
TottemhoeJ ing in the weathered face* and owed

Stone. I " bond " by the workmen - - about 3

L Grey sandy stone in thick beds - seen for 10

The whole of these beds are burnt for lime, and the " Burwell Stone," as it
is sometimes called, is used for building purposes ; its lower portion is only
used for inside work, but the '* bond " rock, if properly dried, becomes very .
hard and makes a good building stone. The foreman here stated that they
had dug to a depth of 15 feet from the base of the bond rock, and were then
stopped by the inflow of water. As elsewhere small brown phosphatic nodules
are common in this upper part of the Tottemhoe Stone, nodules of iron pyrites
occur, and fossils are very numerous and wdl preserved (see list, p. 49), The
Ammonites are chiefly found in the " bono, and also occur in the lower-
most lavers of the overlying Chalk. A similar section to the above is
visible along the N.E. face of the same quarry.

In Mr. Davey's pit just to the south the ''bond" rock does not weather
out quite so distinctly ; it is known, however, to the workmen by its distinctive
characters, and is about 3 feet thick ; the largest block known to have been
obtained from it weighed five tons before it was dressed (a cubic foot of the
stone being calculated to weigh one hundredweight). The blocks are shaped
with a tool somewhat like a two-edged battleaxe, and are allowed to get
thoroughly dry before they are used for building.

Another pit north of that first described showed the following succession : —

Feet.
Soil and rubbly chalk - - - - - 4

Chalk in thin layers - - - - - 10

Tough grey sandy stone in thick bed with many fossils
(Tottemhoe Stone) - - - - - 10

At the Victoria Quarry, between the Windmills at Burwell High Town,
there is a very interesting section, the following beds being shown along the
face recently worked (1878) : —

Feet.
Hard grey sandy stone, in beds of some
thickness, except near the surface,
where it breaks into thin layers - 12

A course of hard sandy stone, containing
Tottemhoe J some iron-pyrites and ftiU of hard
Stone. \ brownish cidcareo-phosphatic nodules,
from the size of a pea to that of a potatoe,
they are brown inside but many have
a greenish exterior coating; fossils
abundant - - - J to 1

Chalk Marl. Hard clunch, marly and blocky - about 15

None of these beds are used for building, and the nodule band is carted
away as rubbish, for it will not bum into lime. The nodules are similar to
those found at Reach, and described by Prof. Hailstonb (see p. 48). A small
fault traverses the pit from N.N.E. to S.S.W., throwing the beds down on
the W. side about o feet. The dip of the nodule bed as seen along the north
face is westward at about 3°, but its tme direction appears to be to the
W.S.W. The workmen stated that in sinking the well at the public-house

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LOWEB CHALK.

west of the pit the nodule bed was pierced at a depth of 22 feet^ thence it rises
to the E.N.E. till near the lime kiln it is onlv o feet from the suiHEace, and
it was said to have cropped out near the pathway leading into the quarry.
The whole of the eastern face, which is not now worked, must therefore belong
to the underlying Chalk Marl, about 20 feet of this being seen.

Ftg, 10,--' Diagram-section through Victoria Pit, BurwelL

Main Road. E.N.E.

Ditch.
W.S.W. i

Hall.

Horizontal scale, 4 inches to a mile. Vertical scale, 100 feet to an inch,
a. Tottemhoe Stone, with nodule bed at base, b. Chalk Marl.

We were told that the well at the windmill to the east was 60 feet deep,
this therefore must pierce nearly the whole thickness of the Chalk Marl, and
the water-supply is probably obtained just above the " Cambridge Greensand."

Nothing like Tottemhoe Stone is to be found in the old quarry belonging to
Mr. Stephens, N.W. of the Windmill, the whole exposed face of which consists
of firm blocky greyish-white clunch for about 30 feet, but the fragments
thrown out of the aeeper holes were bluish and shaly ; near the top of the
northern face are indications of a marly band having a slight apparent dip to
the westward, but this is cut o£E by a fault at the N.E. corner. The whole
section is very like that in the R^h Quarries (p. 48), and is probably in
Chalk Marl.

As &r as can be ascertained it seems likely that the beds quickly become
horizontal, then resume their normal easterly dip, and the Tottemhoe Stone
probably takes the ground again to the east of High Town, and the spring in
the hollow, a mile E.N.E. of Burwell Church, is doubtless an indication of its
outcrop, but beyond this point it has has not yet been traced.

Outliers,

The Tottemhoe Stone is exposed at several points in the long outlier which
stretches westward from Haslingfield. In the old c^^uarries south of that
village the stone is hidden under talus, but it is seen m the newer quarry by
^ihe roadside a quarter of a mile south of the church; the lower part of this
exposes several feet of thick bedded sandy stone, of a greyish brown hue, con-
taining small brown phosphatic nodules, many specimens of Rhynchonella
Mantdliana, and other fossils (see p. 49).

In the clunch pit south of Harlton similar beds of grey sandy chalk are
shown, overlaid by thinner beds of a lighter colour, less sandy and with fewer
fossils.

As the underlying marl is found in the clunch pit near the Wheatsheaf
Inn, the outcrop of the Tottemhoe Stone must pass above this and curve
round toward the Eversden Quarry three-quarters of a mile westward; it would
appear, however, to pass below this quarry, for the chalk here exposed, though
somewhat like Tottemhoe Stone, is not so hard or sandy, and seems to belong
to a slightly higher horizon.

The large quarry above Orwell, some 20 feet aeep, shows rather hard grey
chalk in beds of varying thickness with phosphatic nodules and other organic
remains ; it is thrown down westward by a set of smaU faults. The thicker
beds probably represent the Tottemhoe Stone. Similar beds with phosphatic

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48 GEOLOGY OP THE NEIGHBODBHOOO OF CA31BBIDGE.

nodales occur also in the pit about a mile east of the above, and thence tbe
line of outcrop has been drawn to follow the contour of the hill back to
Haslingfield.

It is quite possible that several outliers of Totternhoe Stone may occur over
the undulating ground N.E. of Cambridge by Teversham, Quy, and Bottishaiii,
but sectional evidence is wanting. The large clunch pits near Reach, ho-w-
ever, disclose the existence of a small outUer resting on the south-western
slope of the hill.

The eastern comer of these ouarries has been recently worked^ and the
following section was observed in 1878 : —

Feet.

Hard grey sandy rock in definite beds, its basement-
bed being very hard and containing many hard
green-coated nodules, the whole called *' brassel "
by the workmen - - - - - 6-10

Blocky clunch, of a lighter colour, less hard and
more marly than the rock above, bedding in-
distinct - - . - - - 4

The dip taken by the nodule bed is apparently about 7° to the W.S.W»
The remarkable layer of phosphatic nodules, by which the base of the Tottern-
hoe Stone is so well marked both here and at Burwell, was first noticed by
Professor Hailstonk in 1816, and is thus described by him : —

*' In one of the pits at Reach a bed of clunch occurs which differs from the
ordinary sort, ana presents some remarkable appearances ; the mass itself is
much harder and is stuck full of concretions of a yellow indurated marl ; out-
wardly they are of a green colour arising from the oxide of iron ; they are in
general kidney-shaped and of all sizes, from a hazel nut to an ordinary
potatoe. The shape of the bed also deserves notice ; its general thickness is
about 15 inches, wnich it preserves for near 30 yards, as appears in the section
of the quarry; it then diminishes at each ena to a thin edge and at length
totally disappears."*

These last words would rather seem to imply the thinning out of a lenticular
bed, but the section then open may have so cut into the Totternhoe Stone as to
show it thinning out upwards on either hand, as the dip brought its base to
the surface. One face is still left, along which it rises eastward, and can be
traced to within about 2 feet of the surface, and the clunch which emerges
from beneath contains two bands of rubbly marl, rising slightly eastward
(along the S.W. face of the ouarry) and then becoming nearly horizontal^
below these are about 30 feet oi greyish blocky clunch with bluish shaly beds
at the base which appear to keep nearly horizontal throughout the rest of the
quarry.

The ^'brassel," as the hard basement layers of the Totternhoe Stone aro
here called, is only quarried to be carted into the Fens for road-metal, for it
does not bum to a good lime.

* Trans, Geol, Socy vol. iii. pp. 248, 249. He also states that the same bed occurs
again at EJaeesworth, '* where it preserves an uniform thickness and direction."

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liOWEE CHALK.

Fossils from the Totternhoe Stone.

Harlton
and Has-
1 lingfield.

Berjrx (fragment) - - - .

Dercetis (? Terebella)

•«•

...

liamna (fragment) - - . -

...

Otodus appendicolatus, Ag, ...

...

Ammonites Lewesiensis ?, Mant,

y, rhotomagensis, Brong, -

...

„ var. Cenomanensis, D^Arch,

...

Belemnites plena, var. Blainv,

„\

!!!

„,

Nautilus elegans, Sby. - - -

...

Ayicula gryphseoides, Shy, - - -

Inoceramns latus, Jfan<.,Yar.Beachen8iSyi?M«r.

...

x"?

...

Lima aspera, ManU . - ^

*••

...

„ globosa. Shy, - - - -

Ostrea acutirostris, NUm, - - -

...

„ cuirvirostrls, var. inflexa, Ether,

...

„ (Exugyra) haliotoidea. Shy, -

• •*

...

„ vesicularis. Lam, . - -

Pecten fissicosta, JB^A^r.

...

„ orbicularis, Shy, ...

„ quinquecostatus, iS^6y«

...

„ Beaveri, Shy, - . - .

...

Plicatula inflata, Shy. . - ,

Spondylus striatus, Shy, ...

.•*

...

Teredo amphisbsena, Goldf. - . -

...

Bbynchonella grafiiana, i>'Or&.

...

„ MantelUana, Shy,

„ Martini, Mant,

<•.

Terebratula biplicata. Shy, ...

• ..

• ••

...

„ semiglobosa, Sby^

„ squamosa, Mant,

...

Terebratulina gracilis, var. nodulosa. Ether, -

...

„ striata, Wahl. - - -

...

Kingena lima, Defr, ....

X
X

Cidaris dissimilis ? (spine) Forhes -

Cjphosoma, ? or Pseudodiadema

• ••

...

1 •••

...

Discoidea subucula, Klein ...

...

Holanter subglobosus, Leske (Shepreth)

Calosmilia? . -

Micrabacia coronula, Goldf, ...

!!!

„\

!..

„,

Onchotrochus serpentinus, Duncan -

...

Serpnia antiqnata, Shy. ...

...

Vermicularia umbonata, Shy,

NSOO.

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■a I ,_.^,.

50 GEOLOGY OF THE NBIOHBOURHOOD OF CAMBRIDGE.

Supplementary List of Fossils from Burwell in the Woodwibdian
Museum, Cambridoe.

Coiux, Aff, Anomia, pap^cea, lyOrb, var.
Notidsnus, Ag. Burwellensis.

Ptjchodus, Aff. Avicula dubia. Ether.

— „ filata,^M«r.

Ammonites Mantelli» var., Sby. Inoceramus striatus, Mant.
„ navicularis, Mant, „ oonvexus. Ether.

„ varians, Sby. ^, var. quadrata^ Ether.

„ var. Coupei, Brong. Ostrea irons. Park.

Nautilus Deslongchampsianus, D^Orb. Pecten elongatus ? Lam.

„ pseudoelegans, D'Orb. Pholadomya decussata, Phil.

„ reflectus {Seely, M.S.) Pinna tegulata. Ether.

Scapliites sequalis, Sby.

Turrilites costatus. Lam. Enoplodytia brevimana, M'Coy.
„ Scbeuchzerianus, Bosc. „ laugei, Mant.

„ tuberculatus. Bosc. Glyphaea cretacea, 3f Coy.

Trigonellites. Necrocarcinus Woodwardi, Bell

(Cherry Hinton).

Aporrhais, sp. Pollicipes gkber, Rom.

Cerithium omatissimimiy Desh. Serpula nistica, Sby,
Dentalium majus, Gardn.

Pleurotomaria (several sp.) Hemiaster Morrisii, Forbes.

Scakria fasciata, Ether. Pentacrinus Fittoni, Aust.

Solarium dentatum?, Desh. Pseudodiadema, sp.

Trochus, sp.
Turbo, sp.

Zone of Holaster suhglohosus.

This zone comprises the entire thickness of the Chalk between
the Totternhoe Stone and the Melbourn Rock ; the whole of it is
shown in the large quarries near Cherry Hinton (close to the line
of section, PI. 6), and parts of it are seen in many other quarries
along the escarpment of the Lower Chalk. There is indeed a
greater number of exposures in this division than in any other
portion of the Chalk of equal thickness^ the reason probably being
that the beds of this zone afford the best material for making lime.

Mr. Whitaker speaks of similar chalk in Buckinghamshire as
coming on above the Totternhoe Stone, and describes it as breaking
up " into large irregular-shaped blocks with more or less curved
surfaces ; ''* in another place he calls it *' marly chalk breaking
•^ irregularly so as not to show bedding."t The Cherry Hinton
chalk might be described in the same terms, and it occurs with the
same general characters throughout Cambridgeshire.

In accordance with the plan proposed at p. 22 we commence
by describing the outcrop near the line of section (PL 6), and will
then trace the zone first to the south-west and secondly to the
north-east from that line.

At Cherry Hinton there is not any very marked line of separation between this
zone and the underlying Totternhoe Stone, and two smfdl slips or fimlts help

* Quart. Journ. Geol. Soc, vol. xxi. p. 400.
t Mem, Geol. Survey, vol. iv. p. 44. (1872.)

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LOWER CHALK. 51

to obscure the junction ; but 3 or 4 feet feom the bottom of the quarry the
rock comes away in smaJler blocks^ which are of a lighter colour^ less sandy,
and less fossiliferous.

The weathered western face exhibits this greyish-white chalky and here the
remarkable irregularity of its bedding is well shown ; this appears to be charac-
teristic of the whole zone^ and has been called false-bedding, but it is not exactly
analogous to the cross-strati£cation so often seen in sands and gravels, for, so
far as our observation extends, the layers are not cut off abruptly, but thin out
more or less rapidly in a lenticular fashion. It is a matter of some doubt
whether this structure can be termed bedding in the true sense of the word.
We question whether it is any proof of current action, and would suggest that
the curved surfaces mav be due to the contraction of a homogeneous mass in
the absence of any dennite bedding planes. We believe, in fact, that they are
lines of jointing rather than of bedding.

That part of the pit which was chiefly Worked in 1875-76 exhibited rather
hard yellowish rock near the bottom (which must have been some 15 or 20 feet
above the lowermost level of the quarry) with fossils in some abundance,
especially Holaster subglobosuSy Plicatula inflata, and Terebratidasemiglobosa, and
passing up into more marly cream-coloured chalk, the whole face being ahout
25 feet high.

In the upper part of the quarry at the southern comer was a freshly cut
face of thick-bedded cream-coloured chalk, the apparent bedding being so
irregular and lenticular that no di^ could be taken. Fig. 11 shows the lower
10 or 12 feet of this face. (Compare Quart. Joum. Geol. Soc, vol. xvii. p.
291.)

JFig^. 11. Sketch of Divisional Lines in Chalky Cherry Hinton Quarry,

The uppermost layers of this chalk are almost white when dry, and contain
very few fossils, Ostrees and ExogyrtB being the most common ; the height from
the middle stage of the quarry to the band of yellowish rock and marl just
below the road at the top of the pit is about 40 feet.

To the southward this zone occupies the ground traversed by Wort's Cause-
way and the Hills Road, and is exposed in the quarry called Shelford lime-kiln
on the Ordnance map. The beds are greyish or creamy-white in colour, and
average from 1 to 2 feet thick, but as at Cherry Hinton they often thicken
out lenticularly from a few inches to 3 or 4 feet. The cliff near the
entrance is 30 feet high, and from this level to the bottom of the pit is about
15 feet; the lowest beds seen are not very hard, but yellowish and gritty.
Fossils are frequent here; we obtained a tooth of Polyptychodon, Holaster sub-
globosus, and teeth of Ptychodus, Lamna, and Otodus; many others were
subsequently collected by Mr. Allen (see p. 54).

The upper part of this zone is again seen in the Shelford clunch-pit on
Steeple Hill, from 20 to 30 feet being shown in the lower part of this quany ;
the chalk is greyish and rather soft, lenticularly bedded and much iointed ;
fossils are fairly abundant. (See list on p. 54).

From this point the grey chalk occupies the flank of the hilly ground N. W.
of Shelford, and runs up {he valley for some distance beyond Stapleford> but is
not exposed in any quarries.

D 2

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52 Gr.OLOGT OF THE NEIGUBOUBHOOD OF CAMBRIDGE.

Passing under the gravels^ which are spread over " Howe Field '' and the
parish of Little Shelford^ it emerges to the west of that village, and sweeps
round the hill-side between " The Well Head " and '' Maggots Mount." Its
upper beds are exposed in the quarries near the Obelisk on this hill, and are
similar to those in the clunch pit near Shelford ; the section here is given on
p. 66. ,

Newton clunch pit, half a mile to the S.W., would appear to be in the upper
part of this zone, it exhibits about 12 feet of hard whitish chalk with imperfect
horizontal bedding ; the beds ar^ about 3 feet thick and split up into blocks
of varying size and hardness ; there are a few nodules of iron pyrites ; Holaster
subglobosus, Terebratula semiglobosa, Kingena Uma, PUcatula inflata, and Ostrea
vesicularis were the only fossils obtained.

The chalk of this zone forms the mass of the hills about Newton and Foxton,
the highest levels only being capped by outliers of the Melboum Rock.

The lower of the two pits S.£. of Foxton shows about 15 feet of rather soft
blocky clunch, the lines of division being very irregular and sometimes nearly
concentric ; a discontinuous layer of rubbly marl was observed in one part of
the pit, and iron pyrites nodules are abundant, some preserving their radiating
crystalline structure, others decomposed into balls of brown earth. The lowest
evel is about 30 feet below the base of the Melboum Marl seen in the higher
pit, and described at p.

At Melbourn from 20 to 30 feet of the same chalk are to be seen in the pits
south of the village, where it is largely burnt for lime ; it comes away in lArge
blocks and is here rather whiter than usual, but the joint planes are stained of
a yellowish-grey colour.

We now return to the neighbourhood of Cherry Hinton, and proceed to
trace the zone along the country northward of the fine of section.

The lime kilns marked on the map, just south of where the roads meet at
Cherry Hinton, are now disused, and the section is partly grown over ; but it
must at one time have exposed the lower part of this chalk and the Tottemhoe
Stone.

Eastwards this division occupies the lower slopes of the hills towards Ful-
boum, and the base is again shown in the clunch pit near Fulboum Asylum.
The well at the asylum is just short of 60 feet deep ; the whole of the hill
therefore on which it stands is composed of the same chalk based upon
Tottemhoe Stone.

The steep slopes which descend towards the village of Fulboum from the
level of the windmill, five furlongs westward of the church, are also made
by the outcrop of this zone, as, too, is the high ground which forms the south-
eastern boundary of Fulboum Fen; just south of Shardelows Well are some old
workings, but these are now quite overgrown. The Fen itself is based upon
the Chalk Marl and Tottemhoe Stone, and the undulating ground which
extends eastwards and northwards towards Great Wilbraham must be occu-
pied by the zone of Holaster subglobosiis, but no good sections are to be found.

Between Wilbraham and Bottisham a long ridge of gravel stretches out
to the N.E., and has preserved these beds from destruction, so that they and
the Tottemhoe Stone underlie the gravel for some distance, but their outcrop
is cut back along the Newmarket Road as far as Spring Hall. Thence they
tum northward and skirt the eastern side of Bottisham Fen towards Swaffham
Bulbeck. Here the zone of Holaster suhglohosus is well shown in two pits
east of the village ; in that facing west, just below the windmill, hard greyish
chalk is seen containing many decomposed nodules of iron pyrites ; fossils
seemed to be scarce, but the characteristic Holaster wslb found. The Melbourn
Rock has recently been disclosed by a fresh excavation in the upper level of
this pit (see p. 59),

The uppermost beds ore again seen in the new pit which faces the north on the
top of the hill ; Holaster subglobostis, Terebratula semiglobosa, Plicatula inflata,

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LOWER CHALK* 53

and Ostrea vesictdaris occur here ; about 15 feet are shown along the eastern
fece, overlaid by a course of yellowish nodular chalk, which dips to the W.S. W. ;
about 10 feet of hard white chalk intervene between this and the Melboum
rock above (see p. 59).

At Swaffham Prior, a quarter of a mile N.E, of the church is a small pit
snowing 15 or 16 feet of whitish irregularly bedded chalk, much shattered in
one place, as if b v small faults or slips ; there appears, indeed, to be a con-
siderable uplift here, for the basement ,;:bed is probably Totternhoe Stone
(see p. 45) ; the upper beds will therefor^belong to the lower part of the over-
lying zone ; they contain Holaster sviMlobosus, Ostrea vesicularis, and a few
other fossils.

From this point the outcrop widens out and occupies the country which is
crossed by the DeviPs Ditch as far as Ditch Farm. The base is seen capping
the Totternhoe Stone in the quarries at Burwell, where it contains Terebratula
biplicata, T. semiglohosa^ T. sqtiammosa, Kingena lima, Rhynchonella Mantel-
liana, Pecten orbicularis, &c. ; thence it stretches south-eastward toward
Exning and Newmarket.

Outliers.

The Grey Chalk forms a long narrow outlier averaging less than three-

?uarters of a mile in width between Barrington and Orwell on the south, and
laslingfield, Harlton, and Eversden on the north.
We have already noticed the quarries along the flanks of these hills in which
the Totternhoe Stone is exposed, and in which some portion of the overlying
clunch is also seen ; there are, however, three pits winch seem to be entirely
above the horizon of the Totternhoe Stone.

The first of these is named Barrington Clunch Pit on the map, and is in
hard greyish chalk with very few fossils, which cannot be very far up in the
zone of Holaster suhglohosus, but the only organic remains found in it, Tere-'
hratula semiglohosa and Ostrea vesicularis, do not give any indication of its
exact horizon.

The next is a small quarnr by the roadside a Quarter of a mile S.S.E. of
Orwell Maypole, which must be nearly 100 feet aoove the base of the Chalk
Marl, and a hard greyish-white stone exposed in the lower part has yielded the
fossils named in the list at p. 54.

Half a mile north of the last-mentioned pit is a much larger one called
Eversden Quany, the base of which appears to be between 70 and 80 feet
above the coprolite bed, for the well at the cottage has a depth of 72 feet, and
is probably sunk down to the base of the marl. The section is as follows (the
fossils found being noted in the list below) : —

Boulder Qay, 3 feet.

Rubbly Chalk, 2 or 3 feet.

Hard grey chalk in irregular blocks, some of large size, the lines of jointing
frequently curved, and in some places slickensided, here and there present-
ing a concretionary structure ; has somewhat the appearance of having
been crumpled or disturbed ; contains many decomposed lumps of iron
pyrites, and seems to dip slightly down the hill to the north, 12 feet.

The hard chalk or clunch exposed in the last two pits is probably the same
as that noted in the Cherry Hinton Quarry, and its horizon there must also
be about 80 feet from the Gault ; there would apjjear, therefore, to be a tolerably
constant bed of hard rock about this level, but its characters are by no means
so well defined as the Totternhoe Stone below.

The highest beds, therefore, in the outlier just desoribed are in the zone of
Holaster svbgldbosus, and nowhere reach the horizon of the Melboum Rock.

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54 GEOLOGY OF THE NBIGHBOUBHOOD OF CAMBRIDGE.

Fossils from the Zone of Holaster Subglobosus.

1 .

•1

«3

Beryx sp. (opercular bones) - - -

Otodus appeadieulatus, ^^. - - .

Oxyrhina Mantelli, Ag, - - _

Odontaspis gracilis, Pict. and Camp

...

Ptychodus decurrens, -4y. ...

Fish vertebreB and coprolites - - -

Polyptychodon interruptus, Owen -

...

Ammonites rhotomagensis, Brong, -

„ varians, Sby.

...

„ var. Coupei, Brong.

■ ••

Scaphites, sp. ? - - . -

...

Avicula gryphffioides, Shy, - - -

Exogyra haliotoidea, Shy. - - -

Inoceramus mytiloides, Mant.

Lima globosa, Shy, ....

Ostrea normaniana, 2>* Orb,

...

„ rauliniana, I)* Orb, - - _

„ vesicularis, Xa»i. - - -

Pecten Beaveri, 5%

...

t, orbicularis, Sby, ...

„ quinquecostatus, Shy,-

...

Plicatula inflata, Shy, ...

Spondylus ssquicostatus, Ether,

Teredo amphisbaena, Goldf. - . .

...

Kingena lima, Defr. - - . .

Rhynchonella mantelliana, Sby,

„ Martini, Mant,

Terebratula biplicata, Sby, . - .

...
X

„ semiglobosa, Sby,

„ sulcitera, Morris

Terebratulina striata, Wahl. -

...

X
X

Cidaris Bowerbankii, Forbes - - .

„ dissimilis, Forbes (spines) -

„ hirudo, Sorig, ...

Discoidea cylindrica, Lam, - - -

Goniaster (plate of ) -

Holaster laevis, var. trecensis, Zeym, .

„ subglobosus, ZcsAc -

Enoplodytia sp. -

Serpulasp. - - - - .

PolUcipes . - - - .

...

Remains of the following reptiles have also been foimd in this zone at the
Cherry Hinton quarries : — Ichthyosaurus campylodon. Carter, Polyptychodon
interruptus, Owen, Pterodactylus sp,, and Saurospondylus dissimilis, fcJeeley.

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MIDDLE OHALK. 55

CHAPTER VL— MIDDLE AND UPPER CHALK.

MIDDLE CHALK.
Melbouen Rock.

The division to which we have given the above name consists of
several thin beds of yellowish laminated chalk with layers of marl,
separated by courses of hard rocky chalk, the whole having a
maximum thickness of 10 feet. These beds are generally to be
found capping the escarpment of the Lower Chalk, or forming the
base of the next rise intervening between it and the Upper Chalk
*scarp.

We have already had occasion to mention the band of yellowish
marl which occurs near the top of the Cherry Hinton quarry;
Df. Barrois, in 1875, was the first to identify this as representing
the horizon of his Belemnites plenus zone, and the subsequent
detection of it in other chalk-pits, has greatly assisted us in tracing
the zones which lie above and below. The best exposures of this
rocky chalk occur near Melbourn and Harston, and the following
is an analysis of a specimen from the latter locality.

Analysis of a Specimen of Melbourn Rock, from Maggot's Mount, near Harston,

Cambridgeshire, by Dr. Frank land, F.R.S.

Insoluble residue on dissolving in acid - '92

Silica 6-44

Sesquioxide of iron and alumina - - 1*51

Calcic carbonate - - - - 87 * 66

Magnesic carbonate - - - - 3*44

Chloride of sodium - - - - -36

Phosphoric anhydride (P2O5) - - - '18

100-51

At Cherry Hinton a narrow band of yellowish gritty laminated marl is seen
m the southern comer, and is let down to the north by a fault with a throw of
4 or 5 feet, two sets of slickensides being shown with about 4 feet of crushed
and disturbed chalk between. This is the basement-bed of the Melbourn
rock, it is not very fossiliferous here, but Belemnites plenus and Ostrea Naumanni
were obtained by Dr. Barrois, and Mr. Allen afterwards found a good speci-
men of the Belemnite in the chalk just below the yellow layer. The height of
its outcrop is about 140 feet above Ordnance datum. The boundary line
sweeps round the hill above Nether Hall and into the combe north of
Wort's Causeway; thence it turns southwards and crosses the Causeway about
a quarter of a mile north-west of the tumulus. A small pit has been opened
here at the north end of the plantation, and the following beds are exposed : —

Feet.
Chalky soil and rubble - - - - 4

Hard chalk with cream-coloured nodules - 2

Two courses of yellowish sandy m^l, separated

by a thin layer of hard chalk - - H

Hard cream-coloured chalk, with Belemnites
plenus - - - - - 3

All these beds probably belong to the zone characterised by Belemnites
plenus, they dip 3'' between S.E. and E.S.E.

The feature made by the outcrop of these beds continues to run nearly due
south, and passes above the Shelford lime-kiln on the Hills Road, thence it
bends westward and sweeps round the hills above Shelford. Steeple Hill is
capped by an outlier of this division, and a complete section of the series of
alternating layers of marl and limestone composing the Melbourn Rock is
shown in the upper level of the Clunch Pit ; this section was as follows in
1875, but it has sincft been cut back considerably.

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56 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE*

Loose chalk, with pockets of coarse gravel -

'"Hard chalk, vnth. wide vertical joints -
Band of laminated buff-coloured marl, Rhyn-
chonella Cuvieri - - - -

Melboum i Hard bedded chalk, much broken by joints ;
Rock. "^ Lamna (tooth), Ostrea veiticularis, Rhyncho'
nella Cuvieri? Rh, plicatilis, and a small
Quartz pebble were found in this bed
(^Sorter laminated chalk with marly layers
Blocky white chalk, Holaster lavis (var. trecensis), Ostrea
veticularis, and Terebratula semiglobosa - - -

Feet.
6
4

The occurrence of the small quartz pebble (which was about an inch lon^) is
remarkable, and recalls the existence of similar stones in the Cambndge
Greensand. The workmen stated that small " cup-bones " (? fish vertebrae)
had been found in one of the marl bands. These bands consist of gritty
laminated marl, in which many lumps and nodules of chalk are dispersed, and
would seem to indicate an interruption of the quiet conditions which prevailed
during the deposition of the beds below.

There appears to be a second small outlier between Steeple Hill and the
main outcrop, but no section is now open. The marl has not yet been
observed anywhere near Stapleford, and the lind on the map has been drawn
in accordance with the general contour of the country and the calculated dip
of the beds.

The hiUy ground which rises up from Dale Moor, north of Sawston, pro-
bably owes its existence to the outcrop of this group of beds, but no exposures
were noticed. Neither is there any sectional evidence for the line by Whittles-
ford and Stanmoor Hall, further than the fact that the chalk seen in the pit
near the latter place resembles the overlying rather than the underlying beds ;
the springs also near Triplow are doubtless thrown out at this horizon.

Although sections along the main outcrop are thus few and far between,
there are several outliers capping the hills wnich rise to the N.W., and in these
there are many clunch pits, some of which exhibit sections of the Melboum
Rock. Thus in the pit near the Obelisk on Magffots Mount, the succession
shown in Fig. 12 was measured at the eastern end. The height of the out-
crop above datum here is about 150 feet.

i^<7. 12. — Section in Chalk Pit Wi of the Obelisk near Hdrston.

Scale, 40 feet to an inch. x x » Faults.

Feet.
0. Chalky soil and broken rubbly chalk - - 6 to 8

^b. Hard bedded greyish chalk, ringing

under the hammer - - - 2 to 3

c. Buff-coloured chiJk, rather soft, in
two or three layers, with marly part-
ings ; Belemnites plenus and Rhyn-

-^ chonella - - - - 3 to 2

d. Hard greyish-white chalk, rocky and
nodular - - - " - IJ to 2

e. Softer grey chalk, with yellowish
stripes, resting in places on a thin
layer of marl - - - ]

/. Rather fiiard P^cream-coloured chalk, irregularly

bedded ------ 4

Melboum
Rock

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MIDDLE CHALK.

These beds appear to dip into the hill on each side, but the dip is increased
at the western end by two small faults, which have let down the beds 3 or
4 feet on the east side. From 15 to 20 feet of nearly white or cream-
coloured chalk, belonging to the zone of Holaster suhghbosus, are shown in
the lower part of the pit, and are burnt for lime.

The shape of Red-land Hill between Harston and Newton is probably due
to a capping of beds similar to those above described ; the steep slope on the
NW. side has been artificially terraced.

Fozton Hill is capped in a similar manner, and the following section is
shown in the higher of the two clunch pits, the beds being nearly hori-
zontal : —

Feet.

Melbourn
Rock ^

6
3

3 +

Loose rubble and thin bedded chalk with traces of
marly bands - - - - about

"Hard creamy-grey chalk
Soffc yellowish laminated chalk

witn some nodules -
Harder cream-coloured chalk,
with enclosed nodules of same
colour - - .

Soft grey mwl, with yellowish
nodules - - -

Hard grey chalk, in beds about
. 6 inches thick, and ringing
under the hammer -
LThin layer of marl
Bedded chalk, weathering along the lines of lamina-
tion, with marly partings, bottom not seen

Returning now to the main outcrop on the S.E., we may notice a small pit
by the road side, half a mile S. of Foulmire (Sheet 47) ; the following beds
are here exposed : —

Feet.
Sandy soil and rubbly chalk - - - 5

f Soft laminated chalk, with layers of

J yellowish marl - - - 2

Hard greyish-white chalk, with nodu-
tiocK. lar lumps - - - - 2

Thin layer of greenish-grey marl, 0.
vesiculariSf about 2 inches.
Greyish-white chalk - - . - l

These beds undulated slightly along the face of the pit, but appeared to
have a general dip of about 3^ to the N.W. ; the spot is beyond the line
we have taken for the outcrop, and the departure from the normal dip may
indicate some connexion with the disturbance to which Wardington Bottom
is due.

At the southern end of Melbourn there are two quanies which exhibit good
sections of the uppermost beds of the Grey Chalk. The succession seen in
the more westerly of these is given below, the beds having a dip of 4"^ to
the S.W., only the lower half of the rock is exposed here ; as follows : —

Feet.
Soil and chalk rubble - - - - about 3

"Hard rocky chalk, weathering

into nodules - - - „ 1

Yellowish grey laminated marl - . „ J to 1
Hard nodular cream-coloured

chalk, with striated surfaces - „ 1 J

Softer laminated greyish chalk
containing numerous speci-
mens of Ostrea vesicularis and
Rhynch, pUcatilis - - „ ftol

Blocky chalk, whitish and tough - -' 4

Tough lenticularly-jointed chalk, shown in
eastern comer of the pit - - - dug to 15

Melbourn
Rock.

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"*iir^

58 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

A similar section is visible in the large quarry a quarter of a mile east, and
the full thickness of the rock is between 8 and 9 feet ; the dip at this point is in
another direction, viz., S. by E. about 5^, and there are several small faults
with a throw of 2 or 3 feet down to the west. The pit was conunenced near the
road in the chalk belonging to the zone of Holaster subglobosus, which there
comes to the surface and is burnt for hme ; it was only as the face was cut
backward that the alternations of hard and soft chalk above became visible ;
these are not used in the kiln as they require a much greater heat for convert-
ing them into lime, and the owner has consequently extended his excavations
westward into the low anticlinal between the pits, where the lower beds come
to the surface.

One of the yellow marl bands may be seen dipping southwards in the railway
cutting N. of Koyston, and at the waterworks in the town hard beds were said
to occur in the well at a depth of about 40 feet from the surface.

The Melboum Rock is again seen in a pit by the side of Ermine Street,
about a mile and a quarter N.N.W. of Royston, the section showing a pre-
ponderance of laminated chalk as follows : —

fr.

8
1
3

^toli
1

1
6

Thin bedded white chalk, rather hard

f Evenly bedded yellowish chalk

I Hard and rough greyish-white chalk
Melboum I Yellowish laminated chalk, with marl
" UnfAr ^ bands - - - - -

^^*^- I Soft-greyish thin-bedded chalk

I Hard chalk, weathering into nodular lumps

LSofter thin-bedded chalk
Irregularly bedded whitish chalk

The softer beds contain many fossils, named in the list on p.

The outcrop of these beds may be traced westward across the fields to the
hill south of Ashwell Street on which the tumulus stands, and they are seen
again in a pit nearly half a mile west of this point. The section here was noticed
by Mr. Whitakeb,* but^t has since been cut back, and the upper beds are now
more clearly shown ; the figure therefore has been slightly altered, and a few
lines added to indicate its present appearance.

Fiff. 13. — Section in Chalk Fit S.S.E. of Litlington Church,

a. Thin-bedded white chalk, rather hard

f 6. Hard cream-coloured chalk, rough and
Melbourn I rocky, in beds about a foot thick, with
a layer of marl at top
Yellowish laminated chalk, with
marly layers and a marked layer of
1^ grey marl at the base

d. Hard massive creamy-white chalk with marly parting

e. Layer of hard cream-coloured nodules, not persistent,

and passing down into iron-stained chalk with
nodules in places - - - - -

Rock. -<

ft.
9

2
9

* Geological Survey Memoirs, vol. iv. p. 45.

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MIDDLE CHALK. 59

Returning now to the point whence we started, where the line of section cuts
the Melboum Rock, it may be traced under the road which leads down to
Cherry Hinton, and followed by contour round the hills between that and the
" Quivers' Charity Farm." Tlie well at this farm is sunk down to the base of
the Tottemhoe Stone, and is 52 feet deep ; the well at Bishop's Charity Farm
is 132 feet deep, the line therefore passes between these two points. It then
bends northward towards Fulboum, and reaches very nearly to the windmill
on the main road above that village ; (see Appendix, p. 160).

From this point it trends to the south, but we have had little else to guide
us beside general contour in drawing the prolongation of the line, though
the spring which rises about half a mile north of Fulbourn Valley Farm
may possibly indicate its outcrop.

Thence it is probablv continued to the north-eastward above Shardelows
Well to the neighbourhood of Wilbraham, for the beds exposed in the cutting
at the junction of the old and new railwavs to Newmarket belong apparently to
the overlving zone. The spring north-east of Great Wilbraham probably
marks its horizon, but the continuation of the main line of outcrop is entirely
conjectural, for though there is a well marked feature, yet we did not fuid any
sections along that part of the country where the marl beds must come to the
surface.

The fact of their persistence, however, is proved by the occurrence of a small
outlier capping the hill east of SwafPham Bulbeck ; the section in the higher
part of the chsdk pit on the west side is as follows : —

Feet,
r Broken chalk and indications of yellowish

Melboum J marly layers - - - - 2

Rock. I Hard rocky chalk, resting on a thin layer

L of yellowish marl - - - 2

Zone of r Bedded white chalk - - - 10

Holaster i Course of hard yellowish nodules - 1

svbglobosm. L Hard white blocky chalk - - 4

These beds appear to dip into the hill towards the east or the north-east.

The yellowish nodular layer is exactly like that seen in the clunch pit at
litlington, and occupies exactly the same position, viz., 9 or 10 feet below
the base of the Melboum Rock. It is interesting to note the recurrence of
this horizon at a distance of 20 miles from the pomt where first noticed, and,
although it does not seem to be continuous over the intervening space, it
shows now similar were the conditions throughout the area in which these beds
were deposited.

A better section of the upper beds is exposed in the larger pit on the north
side of the hill, but only in the south-west comer, for here there is a decided
dip of nearlv 3° to the W.S.W. The hill, therefore, is a synclinal, as is so often
the case. The section in this pit is as follows : —

Feet.

rChalky soil and hard mbbly chalk - 3

) BufP sandy marl - - - 1|
Melboum J Hard lumpy cream-coloured chalk.

Rock. \ Inoceramus labiatus - - - li
I Soft thin-bedded marly chalk, Ostrea

I vesicularis • - - - 1
I Hard white chalk, breaking into small

Zone of I blocks - - - - 10

Holaster «^ Hard nodular bed, with yellowish stains 1
subglobosas, | Blocky whitish chalk, rather hard,

L more than - - - 3

The hill about three-quarters of a mile to the S.E. is probably capped by an
elongated outlier of these beds, and there may be another small patch by the
plantation to the N.E.

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60 GEOLOGY OF THE NEIGHBOUBHOOD OF CAMBRIDGE.

Fossils from the Melbourn Rock.

•-3

o
a 2

IS)

•d.a

Lamii4 subolata (teeth)
Otodus appendiculatus (teeth)
FrotoBphyroena ferox ?, Leidy (tootli)
Cimolichthys ? striatas, Ag, (tooth) -
Fish vertebrfie and coprolites -

Belemnites plenus (type), Blainville -
„ „ long variety

Bxogyra sp. -

Inoceramus sp. (? labiatus, Brong.')

Ostrea Normaniana, J)*Orb,

„ Tesicularis, Lam., (abnndant)-

Rhynchonella Cnyieri ?, I)*Orb,
„ plicatilis, Sbg.f var.

Terebratula biplicata ?, Sby, -
„ semiglobosa, Sby. „

Cidaris (spine) ...

Zone of Bhynckonella Gtmeri,

The road which passes above the quarries at Cherry Hinton cuts
into the chalk which lies above the Melbourn Rock ; this was re-
cognised by Dr. Barrois as belonging to the zone of Inoceramus
labiatuSf but which we prefer to aes^ate by the name of the
RhynchoneUa^ so characteristic of the Sf iddle Chalk and specially
abundant in this zone.

It is a noteworthy, and at the same time an unfortunate, fact that
the pits and cuttings in this part of the Chalk are few and far
between ; possibly it is not found to subserve any useful purpose
and is not worth working : we can therefore only indicate the points
where small exposures are to be seen, but as this zone is comprised
between two well-marked horizons, the general course of which has
been traced on the map, it must occupy the intervening slopes.

The following is Dr. Barrois' description of the beds seen in the road
cutting at Cherry Hinton : — *

Nodular chalky with some small hard nodules set in a greyish paste, a foot.

White chalk, in platy layers, wiljh Inoceramus labiatus and Rhynchonelk
Cuvieri, 3 feet.

The first is probably the uppermost bed of the Melbourn Reck, and the out-
crop mentioned by him below the Tumuli called Two-penny Loaves is probably
that of the same rock, as described on p. 55. No exposure occiurs along the
intervening ground, but the thickness as calculated from the section is between
60 and 70 feet.

* Recberches sur les Terrains Cretacees Superieurs, p^ 166.

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-MIDDLE CHALK* 61

A portion of this zone is exposed in the quarries below Little Trees Hill half
a mile south-west of Vandlebury, the section in the more westerly pit being as
follows : —

Feet.
Chalk rubble, resting on a bed of hard rocky chalk *- - 6

Marly band with chalk nodules, Rhynchonella Cuvieri, Cidaris

spines, &c. - • - - - - i

Bedded white chalk, with several thin layers of laminated
marl ; pear-shaped flints occur occasionally, but the only
fossils found were Ostrea vesicularis and a small Rhyncho-
^ nella, like Cuvieri ----- about 18

Two slips, with a throw of about 2 feet in each case, have let the beds down
to the south. The pit on the south-east slope shows similar chalk in beds
averaging a foot thick. This is the lowest horizon at which any flints have
yet been found in Cambridgeshire, and must be dear the top of the zone ; indeed
the rocky chalk forming: the highest bed in the pit may be the base of the
overlying division.

Following the outcrop westvi'ard up the valley towards Babraham, a chalk
pit will be found in the wood to the north of the cross roads by that village ;
soft white chalk containing Inoceramus labiatus and Rhynchonella Cuvieri is
seen in this, and in the road cutting dose by there is a thin marly band con-
taining loose chalk pebbles or nodules, with a few fossils. This band may be
on the same horizon as that noted in the pit below Little Trees Hill ; it must
at any rate be very near the base of the overlying zone.

The chalk shown in a small pit near Pampisford Hall probably belongs to
some part of this division.

Crossing the Cam to Stanmoor Hall, west of Whittlesford, there is a
small chalk pit in which 8 or 10 feet of rubbly chalk are seen, overlain by
2 or 3 feet of river gravel ; the Chalk here shown is so disintegrated by
the percolation of water downwards from the old river-bed that it mi^t almost
be taken for re-arranged material ; it has a rough lumpy appearance, and the
interstices are filled with chalk detritus stained yellow by iron from the gravel
above ; the hardened lumps of chalk can readily be detached from the matrix,
and good typical specimens of Rhynchonella Cuvieri occur in some abundance,
with fragments of Inoceramus.

Similajr chalk is seen in a pit near Triplow Church, and the base of the zone
is of course seen in the pits previously described near Foulmire and Melbourn.
It likewise overlies the Melbourn Marl in the cutting N.N.E. of Royston, but
this is weathered and overgrown.

Returning now to the point whence we started above Cherry Hinton, the
beds of this zone must crop out along the northern slopes of the Gog-Magog
Hills by Bishop's Charity Farm, and the chalk seen below the rock-band in
the clunch pit on Missleton Hill belongs either to the uppermost part of this
or to the base of the overlying zone.

No other exposure occurs till we reach the cutting on the Cambridge and
Newmarket line, a mile S.E. of Great Wilbraham; this was widened in 1875,
and the following section exposed : —

Light-coloured sand with flints - - - about 6 feet.

B^ded white chalk without flints, containing Inoceramus-
labiatus, Terehratula semiglobosa, and Echinoconus
globulus . - - - . about 15 feet.

In the gravel and chalk pit half a mile to the south disintegrated rubbly chalk
without flints is seen to a depth of about 8 feet. Beyond this point there are
no chalk pits in this zone, and patches of gravel conceal some portions ; but it
probably occupies the ground by Allington Hill Hare Park, and Newmarket
Heath.

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62 GEOLOGT OP THE KEIGHBOUBHOOD OF CAMBEIDGE.
List of Fossils from the Zone of Rhynchonella Cuviebi.

Ptychodus decurrens ?,Ay.'

Inoceramus mytiloides, Mant, lablatns
Brong, - - .
„ var. problematicug, D*Orb, '
Ostrea vesicularia, Lam, - -

X
X

X
X
X

X
X
X
X
X
X

X
X

Rhynchonella Cuvieri, D'OrL (type)
„ „ var. (or young)
^ Mantelliana, Sby,
„ Martini, Mant.

Terebratula semiglobosa, Shy.

Terebratulina gracilis, Schlotk, var. lata, Ether.

X
X

Cidaris dissimilis ?, Forbes (spines) -
Echinoconus globulus - - -
„ subrotundus, Mant.

Serpula antiquata ?, Sby. - - -

X
X

Zone of Terebratulina gracilis.

Referring again to the line of section across the Grog- Magog
Hills (Plate 6), it will be seen that a marked rise of the ground
occurs by the tumulus marked on the Ordnance maps above the
end of Worts Causeway; this seems to be caused by the outcrop
of some hard beds which appear to underlie the higher part of the
Wandlebury district, and to form the base of the Terebratulina
gracilis zone.

By combining the information acquired during the sm'vey of
the district with that obtained in running the line of section, we
have found it possible to indicate the outcrop of these beds by a
line which maybe taken as generally correct, though it has no
more pretensions to detailed accuracy than any of the other zone-
lines on the map.

By a reference to the map (Frontispiece) it will be seen that this
line exactly circumscribes the numerous patches of gravel which
cap the Gog-Magog Hills, and it is probably as much owing to the
existence of this hard rocky chalk, as to the protective influence of
the gravels, that these hills have resisted denudation and assumed
their present form.

The continuation of this line to the N.E. is taken outside a
series of sections in which the fossils characteristic of this zone
have been found, and along the flank of what may be called the
third step in the chalk escarpment ; this is doubtless caused by
the persistence of similar hard beds along its course, but the
evidence in Cambridgeshire is not sufficient to make it clear
whether there is any deflnite and constant bed which can be taken

Digitized by VjOOQ IC

MIDDLE CHALK. 63

as forming the base of the zone. The question too of the further
subdivision of the Middle Chalk is one that cannot be solved in
Cambridgeshire, though there would certainly appear to be palaeon-
tological evidence for separating off the upper 50 feet of this zone,
and constituting them into another division. We propose there-
fore to describe in the first place those sections exposing the lower-
most beds of the zone, and subsequently those in the upper division
below the Chalk Rock.

Lower Dimsion or Vandlehury Beds,
These beds are not exposed along the line of section across the Gog-Magog
Hills, but they are to be seen in the chalk pit near the top of Missleton Hill,
a mile S.W. of Fulbourn, where the succession is as follows : —

Feet.
Gravelly soil and chalk-rubble - - - - 3

Hard nodular chalk, with yellowish stains and semi-crystal-
line nodular lumps (many fossils) - - - 4
Massive white chalk, Inoceramus Idbiatus - - - 7
Platy chalk, with a layer of grey marl - - - OJ
Massive white chalk with a few flints and many fossils,
TerebratvUna gracilis common - - - - 8
Taking the layer of marl as an indication of the bedding, the dip is found
to be 6° or 6° to the E.S.E.

If the hard rocky chalk at the top of this pit be taken as the basement-bed
of this division, the massive white chalk below must of coiu*se be classed with
the underlying zone of Rhynchonella Cuoieri ; the whole section is indeed very
like that in the quarry at Little Trees Hill (see p. 61). Hard rocky chalk
occurred there in a similar position, and if this should prove to be a persistent
layer it might receive the name of the Wandlebury Rock.

Missleton Hill is formed by a small outlier of this rock, and the small conical
hill to the southward appears to be just capped by the same bed, which pro-
bably takes the ground again north of Fulbourn Lodge and underlies the nilly
ground to the south, though we cannot point to any other spot where it fs
actually exposed.

In the small pit north of Fulbourn Lodge 10 or 12 feet of bedded white chalk
are shown, containing Terebratulina gracilis B,nd Rhynchonella Cuvieri; and
the little knoll called Megs Hill, three-quarters of a mile south of the Lodge Farm,
exposed similar beds, an excavation on one side showing hard white chalk
with a band of marl containing Terebratulina gracilis. Another small pit
occurs at the eastern comer of the plantation on Signal Hill.

The section in the road-cutting leading N.E. from Babraham has already
been mentioned ; the band of marl here shown may be the same as that at
Megs Hill, but there are so many marly layers in the Middle Chalk that it is
unsafe to attempt any correlation at present ; this layer is however remarkable
for containing Rhynchonella Mantelliana, and Rh, Martini which have not else-
where been found above the Melbourn Rock.

The railway cutting near Babraham is too overgrown for the chalk to be
well seen, and the next exposure is in a small pit on the hill slope south of
Little Abington Grange. Here rather hard white chalk is seen, somewhat
blocky, and not very distinctly bedded, but broken up by strong vertical and
inclined joints, the sides of which are much iron stained, but this colouring is
probably due to the gravel capping the hill above ; a few silicified Ventriculites
occur, but no other flints were to be seen, and fossils were scarce.

Beyond this we cannot indicate the course of the zone with any certainty,
but we should expect it to occur in the neighbourhood of Pampisford HaU,
where the hills present a steep 'scarp like that which borders the Gog-Magogs.
Thence it probably runs back for some distance up the valley of the Cam, but
we have nowhere observed any exposure.

Near Royston there are two quarries which give good sections of this part
of the ChaJk. Since the surface at the Royston Waterworks appears to be
about 40 feet above the Melbourn Rock (see p. 68), the floor of the deeper of
these pits, about two furlongs to the S.E., cannot be much above the same
level ; the section here is as follows : —

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64 GEOLOGY OF THE NEIGHBOURHOOD OF OAMBBIBGE.

Feet

Thin-bedded chalk, yellowish (? stained f^m above) with

scattered elongate and root-like flints - - - 12

Layer of greyish laminated marl, 3 inches.
Massive wick-bedded chalk with a line of scattered flints at
the top - - - - - - * \6

Layer of iireffular flint nodules.

TMck-bedded white chalk 8

These beds dip slightly S.E. The only fossils found were Discoidea Dixoni,
Mieraster sp. and lAma spinosa.

At the lime-kiln, 3 furlongs S.W. of the Church, a similar section is shown ;
the chalk dipping at 5° to the S., and containing scattered flints of a round or
oval shape ; many of these when broken open were found to enclose Siphoni-
form sponges. Inocerannu Brongniarti, Lima spinosa, and TerebraMa semi-
globosa were obtained here.

Returning now to the sections on the north side of the line of section,
the first we meet with is the cutting on the abandoned railway near Worsted
Lodge. This exhibits bedded white chalk, with occasional irregular flints in
rather indefinite bands ; these flints have assumed very remarkable forms, being
mostly long, narrow, and root-like, many are nearly cylin^cal, and often lie
almost vertically in the chalk, as if they were sponges silicified in the position
of growth, but others are of very irregular form.

The harder beds stand out from the rest, and appear to be dipping east; they
contain fragments of Inocerami, and other fossils are not rare, the most notable
being Echinoconus subrotundus, TerebratuUna gracilis, young Rhynchanella
Cuvieri, and a species of ParasmiUa,

In the next railway cutting at Mutlow Hill similar beds are traversed, but
they would appear to form an outlier, the main outcrop coming on further east
near Bedford Gap ; this cutting is about 12 feet deep in laminated white chalk,
breaking up into small brick-shaped fragments ; flints occur scattered irregu-
larly along one or two lines ; towards the N.E. end some hard beds crop out,
like those near Worsted Lodge, and appear to dip slightly to the south, though
the real dip may be S.E. ; they contain flints, Inocerami, and other fossils.

These hard courses must lie somewhere near the base of the zone, and it is
possible that they are on the same horizon as the Vandlebury Rock, though
they are somewhat different in character.

Upper Division,

The upper part of this zone appears to consist of soft white homogeneous
chalk, witn occasional layers of marl ; flints are abundant at certain horizons,
but there are spaces 10 feet or more in thickness, which do not contain any.
Many of the flmts assume curious forms, and silicified sponges and Ven-
triculites are generally common.

There are very few exposures of these beds in our area, but they form the
slopes below the outcrop of the Chalk Rock, and may perhaps be regarded as
an expansion of the zone of Holaster planus ; this, nowever, is a point that
requires further investigation, but palseontologically they certainly appear to
be linked to the Chalk Rock rather than to the zone below.

The quarry which is nearest to the line of section is at the lime kiln, marked
on the Ordnance map north of Linton ; in this white bedded chalk without
flints is exposed ; some of the fossils belong to species which are now met with
for the first time, such as Micraster cor-bovis i^ &nd Holaster planus: Ven-
triculites too are common, and the fiiuna approaches to that of the Upper
Chalk, so that these beds are probably not far below the Chalk Rock.

The chalk exposed in the pit east of Great Chesterford, described in the
Memoir on Sheet 47> p. 6, belongs probably to this division.

Near Ickleton, on the west side of the Cam Valley, there are two pits in the
higher part of the Middle Chalk ; the first of these is six furlongs S.S. W. of
Ickleton Church, and shows thin-bedded white chidk with a few scattered
flints. Ventriculites are common, but other fossils scarce. The second, a mile
and a half W.S.W. of Ickleton, is in similar chalk, and yielded the following
fossils; Scaphites eequalis, Inoceramm Cuvieri? and Terebratula semiglobosa.

Returning to Sheet 51 no pit or exposure of any consequence is met with
for some distance to the northward of the section line ; about a mile east of

Digitized by VjOOQ IC

MIDDLE CHALK.

Six-mile Bottom Station, and just beyond Westley Lodge, there is a pit in
which the following beds are seen :—

Feet.
White chalk, rather broken, without flints, but with a few

nodules of iron pyrites near the bottom - - - 12

Thin layer of grey clayey marl - - - - J

Whit« bedded chalk, full of finger-like flints of aA\ sizes, with
a few more massive nodules - - - - 6

A short distance N.E. of Dullingham Station is another quarry in which
similar chalk is shown, as follows : -

Feet.
Bedded white chalk without flints - - - - 4

Thin bedded chalk, with many flints of various sizes, some
long and in-egular, others thin and flattish, and others large
and nodular - - - - - - G

White chalk, rather hard, without flints - - -10

The very uppermost beds of the zone are shown in some of the pits where
the Chalk Rock is exposed, and are mentioned under that head.

Fossils from the Zone of Terebratulina gracilis.

Lower Beds.

Upper Beds.

a
S

if
l|

estley
Waterless
(two pits).

3 O

Scaphites sequalis ?, Sby (Ickleton).

Inoceramus Brongniarti, Sby.

...

„ mytiloides, Mant,

„ problematicus, D^Orh, -

Lima spinosa, Sby, - - -

...

„ striata, Shy

Ostrea vesicularis, Lanu -/

...

Pecten Beaveri, Sby. - - -

...

Rhynchonella Cuvieri, VGrb.

„ „ var. (or young)

„ plicatilis?. Shy,

...

„ Reedensis, Ether,

...

Terebratula semiglobosa, Shy,

Terebratulina gracilis, ScJdoth. - T
var. lata, Ether - j

„ striata, WahL -

...

Cidaris dissimilis, Forbes (spines)

„ sceptrifera, Mant.

...

Cyphosoma radiatum, Sorig, -

...

.••

...

Discoidea Dixoni, Forbes (Abington).

Echinoconus subrotundus, Mant,

...

Holaster planus, Mant.

...

Micraster breviporus, Ag,

...

„ do. or cor-bovis, Forbes -

...

X
X

FarasmiUa sp. . - _

„ impressus, Smith

...

Dercetis (? Terebella)

N309.

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66 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

Chalk Rock.

The[Mi(ldle Chalk passes upwards into a band of hard crystalline
chalk, which Mr. Whitaker has named the ^^ Chalk Rock." It
may be traced, perhaps with slight breaks, quite across this district,
its line of outcrop constituting the division between the Middle and
Upper Chalk.

The rock is shown less distinctly than elsewhere where the line
of section crosses the area, but the position we have there assigned
to it may be taken as approximately correct. Following the method
adopted at p. 22, the sections will be noted in order to either hand
from the line of section.

To the south and west the outcrop passes through Linton, then
sweeping round by Abington and Great Chesterford Parks, it
runs along the eastern flank of the valley, which it crosses to the
south of Chesterford. Rising again on the other side it follows a
line roughly parallel to that of the Boulder Clay, but for several
miles its course is not distinctly defined. It passes west of Heydon,
near Chishall and Barley, whence to the edge of the map north
of Tharfield it follows a line of disturbance.

To the north and east from the line of section the Chalk Rock
runs to Balsham, thence, following the shape of the ground, round
by Congers Well and Linnet's Hall to Westley Waterless ; beyond
that village, and about a mile west of DuUingham, it passes under
the Boulder Clay.

Analyses of two Specimens of Chalk Rock from near "Newmarket (51 S.E.),
by Dr. Frankland, F.R.S.

Composition in 100 parts.

Moisture at 100° - - - - -13

Organic matter - - - - '32

Sesquioxide of iron, partly present as protoxide • 64
Alumina ----- '62
Calcic carbonate - - - - 97*25

Magnesic carbonate - - . Trace.

Phosphoric anhydride (P2O5) - - '2'

Moisture at 100° -

Silica

Sesquioxide of iron -

Alumina

Calcic carbonate

1-hosphoric anhydride (Pj

O5)

99-17

- -20

- -31

- -69

- -64

- 98-67

- -20

100-61

Both to the north and south of Linton, the line has been traced solely by
the lumps of hard chalk (resembling the rock as seen elsewhere) found on the
surface. About three-quarters of a mile west of the railway station the line is
lost beneath the Boulder Clay, and is shown as following the shape of the
high ground by Abington Park. A mile south of this place it again comes to

Digitized by VjOOQ IC

MIDDLE CHALK. 67

the surface^ but passes under the clay again almost immediatel;^, just^ running
through a chalk pit in which a good section is shown ^with a slight dip to the
south.

Feet.
Chalk with flints- ..««.. 6

f An irregular layer of rubbly crystalline yellowish Chalk, '
Chalk in lumps enclosed in a marly matrix, and containing
llock. -^ fossils, phosphatic nodules, and decomposed pyrites - ^ 2 to 5

Marly Chalk

Hard crystalline Chalk, passing into the bed below
Soft tabular Chalk, with few flints - - - - 10

The upper surface of the Chalk Rock presents a definite line ; the lowest bed
passes gradually into the soft white Chalk below, and varies from a few inches
to a foot in thickness.

On the hill flank, east of Great and Little Chesterford, hard Chalk again occurs
at the surface, and half a mile east of the latter place a fair section of the rock
may be seen by the roadside.

From this point, for several miles westward, the Chalk Rock is not exposed,
the numerous pits in the Chalk near where it occurs being either above or
below its horizon.

There is a pit S.W. of Heydon, in which the Chalk Rock (?) is shown dipping
a little west of north at an angle of 25° ; south of Barley it dips 40° in the same
direction • Further westward the dip is found to have increased to 60°, still
west of north, but another pit still further westward shows a dip of 22° only,
and due north in direction.

The last-named three pits, all evidently on a line of flexure or
disturbance, are so situated that a semicircular curve passing
through them just encloses the head of the valley called Wardington
Bottom, the initial cause of which is probably this downthrow (or
rather depression) of the Chalk. The pit S.W. of Heydon is
probably not on, but somewhat to the south of, the line of greatest
flexure ; the other three pits all present exposures of the Chalk
Rock, which fact is somewhat remarkable. These sections have
already been described, and the line of flexure noticed in the
Memoir on Sheet 47 (pp. 7-11, Figs. 1 and 2).

In the pit at Smyths End, and in that north of Reed, it is re*
markable that, notwithstanding the high angle of dip, the Boulder
Clay is resting on a surface of the beds nearly parallel to. their
stratification. At first sight this fact would seem to indicate that
the clay was deposited upon them when horizontal or nearly so,
and that the disturbing force had acted on the beds in Post-glacial
times ; but it is more likely that during the Pre-glacial cutting
back of the escarpment, and after the bendine of the Chalk, the
beds slipped off each other in masses along the planes of bedding,
and that the Boulder Clay was deposited against the slope thus
formed. The tongue of Boulder Clay protruding from the edge of
the main mass to the pit north of Barkway (see Fiff. 2, p. 8, Geol.
Sure. Memoir, on Sheet 47) offers no evidence either way, as it
seems to have been forced in under a mass of rubbly chalk. Such
sliding down of the beds, probably in large masses, as denudation
went on, would materially lessen their cohesion, and render them
more easy of removal by water than the parts not so disturbed on
either hand. The escarpment would be more rapidly cut back at

K 2

Digitized by VjOOQ IC

68 GEOLOGY OP THE NEIGHBOUBHOOD OP CAMBEIDGE.

this spot than at others, until a point was reached where the beds
folded back into their normal position ; in two of the pits this
point is exhibited.

Passing to the north and east from the line of section we come to the site of
an old Clunch pit, marked on the Ordnance map, now filled in and overgrown ;
but its name implies a bed of hard chalk, which is probably the Chalk Roclt .
The line is drawn through this pit, by Balsham, and on to the high ground,
where, 1| miles N.W. of that village, hard crvstalline Chalk is scattered over
the surface of the fields. The same indications occur just west of Conger's
Well, and by the roadside, a Quarter of a mile north of Wratting Grange, there
is hard crystalline yellow chalk, which doubtless is Chalk Rock. Similar Chalk
is seen in the bank, near the top of the hill, by Linnet's Hall, and from this
point the line runs by contour to a pit a quarter of a mile S.E. of Carleton
Grange, which is partly grown over, but from one face it has been tunnelled
in several directions, the Chalk Rock, about 3 feet thick, forming the roof.

A little further on, in a pit three-quarters of a mile S.W. of Westley
Waterless, the following section is seen, in which the rock can at once be
identified : —

Feet.

Upper Chalk, with flints ------ 8

Chalk Rock ; crystalline jrellowish Chalk, much broken up ; the
top presents a definite line, the base passes down into tne bed
below 2 to 3

White Chalk, with few scattered flints.

The beds are horizontal.

There are three pipes, two filled with gravel, the other with brown and grey
clay. These run down through the Chalk Rock into the Chalk below.

North of this and half a mile N.W. of Westley there is another pit which
appears to be on the same horizon, though the rock here is not so compact or
so clearly marked as elsewhere ; the section is as follows : —

Feet.
Hard chalk with several yellowish layers, near the base containing

lumps of hard ctystalline chalk and flint nodules of irregular shapes 15
Two thin layers of tabular flint with white chalk between - - 2

White chalk with a few flints - - - - - 5

The dip is about 2° to the S.E. At the S.W. and N.E. corners of the
quarry the layers of tabular flint cease to be continuous, and pass into lines of
nodules. The fossils obtained from the hard chalk above are those which are
elsewhere found in the Chalk Rock (see list below. No. 2).

In the next pit to the N.E., two furlongs W. of Stetchworth Church, a more
distinct band of hard yellowish crystalline chalk is exposed at the bottom, and
contains a similar assemblage of fossils.

The Chalk above contains flints arranged in regular and horizontal layers,
but some of the flints are remarkable for their great length ; these measure
two feet or more, and pass vertically through the beds of chalk, bulging
slightly at the divisional planes between the beds. From this chalk the fossils
listed on p. 69 were obtained.

Digitized by VjOOQ IC

MIDDLE CHALK.

Fossils from the Chalk Kock.

£• .

12 cT

7 tt

1 1

Amnioiiltea ProspcHartus, IT Orb.

Beaphitetj seqwalis?, Sb^,

*..

...

Turbo gemmatuBjSAy^

Soljirium, &p^ . - -

Pleurotomaria perspectiva, Mant,

Inoceramus Brongniarti ? -

...

lima spiuosa, Sbrf. - _ _

***

ff lioperij 3Ian£.

*..

Ostrea, sp. -

■■*

Hhynchonelk limliatii, Schloih.

„ plicaiilisj Shy.-

...

„ Reedensisj Etlmr,

...

Terebratiila carnca, Sby.

„ semiglobosa, Sbg.

...

Ananclijtes ovatus^ Leshe

Hoi aster planuBj Mant.

.^.

Mcrast^^r corbovis, Forbes -

1»*

„ cor-anguiouTU, Leske^ yar.

...

,, breviporus - _ _

...

,L.

...

Cidarkj sp. (^spiiie) ^ - -

Parasrailia ceatralfj? ?, Mant,

Yentriculites raannmillaris, Smith

„ mdiatus, Mmtt.

...

ft impresfius, Smith

The first two colamns are taken, with corrections and additions, from the " Geology
of the N.W. part of Essex, &c.,'* p. 9. — Geological Survey Memoir ^ 1878.

UPPER CHALK.

Zone of Micraster, Cor-bovis.

Towards the close of the period of the Middle Chalk thei^ was
probably a slight upward movement of the sea-bottom, or a some-
what different distribution of sea and land. The change was
gradual, as is indicated by the Chalk Rock, which passes up from
the pure white chalk, into a hard and more or less crystalline or
compact rock, tinged slightly yellow by the j^resence of a small
percentage of oxide of iron.

A still further change caused a cessation of this deposit, and
perhaps an erosion by deep currents over a greater part of the
area. The sharp line of demarcation between this rock and the
overlying Upper Chalk seems to indicate such conditions. During
the period in which the Upper Chalk was deposited, the water must
have been equally, or even more, charged with silica, which it
threw down in a different manner, as it is now found as flint in

Digitized by VjOOQ IC

70 GEOLOGY OP THE NEIGHBOUBHOOD OF CAMBBIDGE.

numerous horizontal bands of nodules and thin tabular layers.
The tabular flint in joints and fissures was probably formed after
the consolidation of the chalk, and may be forming e?en at the
present time.

As regards the occurrence of flints in regular layers in the
Chalk, we would make the following suggestions. It is generally
believed that every nodule of flint has been formed around some
organic nucleus, and this may or may not be the case ; but it is at
all events probable that decomposing organisms attract and retain
silica from solution. When the chalk was first deposited it must
have been in the form of a soft calcareous mud, much less dense
than in its present condition as chalk, a foot of which represents
several feet of the substance in its earlier state.

The silica now found as flint would at that time have been
equally distributed throughout the water by which the unsolidified
portion of the mass was permeated.

We may assume that the surface of this mud was at some particular
period strewn with organic remains in varying stages of decomposi-
tion. It matters not (for the purpose of this argument) what
chemical actions were set up, or how they were originated, since we
find that the silica was precipitated or deposited in and around the
organic remains on the sea-floor. And when once in action the
process, whatever it may have been, continued, and the silica ac-
cumulated along the same plane of decaying organism, notwith-
standing the mud that was still being thrown down, and by which
the forming line of flints was buried. We assume that the force,
whatever it may have been, would act upwards and downwards
through some definite thickness. of the mud, and that until the
sediment had attained a certain height above such line, the silica
would continue to segregate along it, in and around its organisms.
When that point was reached no more silica would segregate along
that particular zone, the organic remains on the then existing
floor would in a similar manner serve as the nuclei of a new layer,
and another line of flints would be at once commenced.

As the sediment increased, consolidation proceeded, and the
deposit varied in density throughout^ firom the compressed chalk
with layers of flints to mud in which flints were bein^ formed at
and near the surface. This fact is worthy of attention, because
any irregularity in the surface (or other plane along which flints
were formed) would be very considerably modified on compression.
If one foot of chalk represents 10 feet of the original mud, any old
hollow or ridge, varying from a plane to the extent of 10 feet in a
given distance, would now vary from that plane one foot only in
the same distance^ and such variation would perhaps be scarcely
perceptible.

The organic remains found as fossils in the Chalk are not neces-
sarily in layers, indeed they are constantly found without regard
to any such definite arrangement ; their position, therefore, will not
explain the fact that the flints are so frequently found in regulai*
and parallel lines. There are, we admit, many difficulties in the
way of the foregoing explanation, still we venture to suggest that
as it indicates a new point of view from which this question may
be regarded, it is worthy of some consideration. What we say is

Digitized by VjOOQ IC

UPPER CHALK. 71

this, that once given the initial plane of segregation, the force
(whatever it may have been) by which the silica was attracted
would act only through a constant thickness of similar deposit^ and
that the layers of flints so formed would in consequence preserve
an approximate parallellism.

Only a very small portion of the area described in this memoir is
occupied by the Upper Chalk, except where it occurs beneath the
Boulder Clay. The boundary of the latter runs roughly parallel
with, and at no great distance from, the outcrop of the Chalk Rock,
leaving exposed a narrow belt only of the Upper Chalk.

There are many pits and sections in which the chalk is exposed,
owing probably to its value, in former times if not now, for spreading
over the surface of clay lands ; certainly many pits occur quite
near to the clay boundary. The chalk presents the usual characters,
being a soft earthy limestone^ with occasional bands of harder or
more siUceous chalk, and layers of flint, either tabular or in nodules.
With few exceptions the deposit lies in a horizontal position, or
nearly so ; where any dip is obtainable it is generally in a S. and
E. direction ; the one notable exeption being the line of flexure S.
of Royston, see p. 67.

Proceeding, as before, from the line traversed by the section, westward by
Linton, the Upper Chalk with a few flints is seen in the railway cutting ;
again in a pit by Hadstock, and is then lost under the Boulder Clay. It is
not shown again on this side of the Granta, except in one pit, where it emerges
S. of Great Chesterford Park.*

Between Chesterford and Heydon several pits are found, in all of which the
Chalk contains flints, and appears to be horizontal ; N. of Heydon it is so, but
from this point commences the deflecture to the N. previously described. The
Upper Chalk is seen in all the pits through which the line of disturbance runs,
and in several others between that line and the Boulder Clay. It has almost,
if not quite, resumed its horizontal position before passing under the clay,
although in one case, half a mile S.£. of Smyth's End, it still retains a dip to
the N. of 12 degrees.

These, and some pits near Tharfield, have been described in the memoir on
Sheet 47.

On the E. of the section line, a pit between Ashdon and Bartlow gives the
following section : —

Feet.
Boulder Clay (at one corner only) - - - 2

Sandy clay, with stones - - - - 1 to 2

Upper Chalk, with flints and thin marly bands ; beds flat.

At the top of the Chalk is the hard crystalline band, 3 inches thick, so often
found at the base of the Boulder Clay where resting on Chalk. (For remarks
on the origin of this hard bed, see Memoir on Sheet 47, p. 60.)

About a mile and a half to the N.E. are two other pits, exhibiting good
sections.

At the " Middle of the World,'* a mile S.W. of West Wickham, are some
pits in Chalk, with few flints, bedding horizontal, while another pit half a mile
W. of that village shows similar chalk, with tabular flint in many diagonal
joints, and dipping 3 degrees to S.E.

The limekilns just N.W. of Balsham give a good section ; the flints are not
numerous, but they enclose an unusual number of fossils, Spondylus spinosus
being abundant.

Another pit N.N.E. of Balsham and half a mile N.W. of West Wratting shows
chalk with layers of black flint, and tabular flint in many diagonal joints, the
bedding being horizontal.

* See 3Explanation of Sheet 47, p. 7.

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72 GEOLOGY OP THE NEIGHBOURHOOD OV CAMBRIDGE.

The sections near West Wratting and Stetchworth, exposing the base of the
Upper Chalk, have already been described. An old pit about a mile S.E. of
Carleton Grange is probably above the Chalk Rock. The only fossil found
was Epiaster gihhus.

List of Fossils from the Zone of Micraster corbovis.

;§

goo

Inoceramus Cuvieri ?
Lima Hoperi, Mant. "
„ spinosa, 56^. -
Pinna decussata, Gold/.

Rhynchonella plicatilis, Sby.

Terebratula camea ? Sby, -

„ semiglobosa, Shy,

TerebratuUna striata, Wahl. -

,, gracilis, Scloth,

Ananchytes ovatus, Leske -

Cidaris sceptrifera, Mant.

Cyphosoma radiatum, Sorig, -

Micraster cor-anguinum, ? Leske
„ corbovis, Forbes -
„ cortestudinarium, Go/<(/*. (var.brevis)
„ (Epiaster) gibbus, Lam. -

Farasmilia centralis, Mant.
Ventriculites, sp. ? -
Coscinopora globularis, Phil.-
Alecto, on Micraster corbovis

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GLACIAL DEIFT. 73

CHAPTER VII.
GLACIAL DRIFT.

Between the Upper Chalk and the next newer formation occur-
ring within the limits of our district (map, plate 7), there is
a very great gap. All the Tertiary beds are absent ; all traces of
them have been removed, unless thefew green-coated flints described
as occurring in a small pipe in the Chalk be a trifling exception
(See Explanation of Sheet 47, p. 10).

Neither do we find any of the earlier Glacial deposits, although
these occur a few miles only to the south ; but, as has been
remarked by one of us, '* the gravels can in no instance be traced
up to the escarpment of the Chalk, or, in other words, beyond a
certain definite level. It is not that they disappear beneath a
great tl^ickness of Boulder Clay to reappear at its opposite
boundary; on the contrary, it is evident that they gradually thin
out, and a few miles before the escarpment is reached we find
the Boulder Clay overlapping them, and resting directly on the
Chalk."*

There are a few unimportant exceptions where local deposits
of gravel occur at or near the base of the Boulder Clay, but these
are not to be regarded as the representatives of a distinct period or
of a set of physical conditions differing from those by which the
cIot was produced.

The line of section, Plate 6., intersects one of these local
patches between Ashdon and Bartlow, where the railway cutting
shows a thin bed of sand between the Chalk and the Boulder
Clay ; in the brook about half a mile to the S.E. a thin bed of
gravel occurs in the same position ; in the chalk pit, noted on p. 71,
it has thinned out to a mere sandy base to the Boulder Clay.
A similar bed of gravel occurs beneath the Boulder Clay on the
N. side of the village of Hadstock ; the two are probably con-
tinuous beneath the Boulder Clay.

Another possible exception is in the Cam Valley, at Chester-
ford, where loam occurs in connexion with and probably under
Boulder Clay, and an extension of the same, or equivalent, deposits
at Whittlesford. For a description of the former the reader is
referred to the Memoir on Sheet 47, p. 39.

Boulder Clay.

This deposit covers the western side of the district, skirts its
southern margin (that is, the Chalk escarpment), caps the Chalk
outliers of Orwell and Coton, and the ridge N. of St. Ives, and
occurs in isolated patches at various levels.

The clay on the top of the Chalk range is the edge of the wide
sheet which covers large parts of Essex and Hertfordshire. It
presents a very irregular boundary, which, however, conforms
generally to the contour of the ground, but in some cases, where

* Penning, Quart. Journ. GeoL Soc., voL xxxii. p. 191.

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74 GEOLOGY OF THE NEIGIIBOUKHOOD OF CAMBRIDGE.

the clay occupies an old slope or channel^ it runs out in long
tongues or down to lower levels. In one instance, to be more
particularly referred to hereafter, about Hildersham and Abington
it rests on an old sloping surface, from the top of what may be
called an outlying part of the escarpment down to the valley
below. The small outliers at some distance from the main mass
are also at considerably lower levels. The reasons for this, and the
conclusions drawn from the mode of occurrence of these remnants,
willpresently be considered.

The Boulder Clay has several constant characteristics, and some
that vary according to local circumstances. It never shows any
signs of stratification ; in section it is hard and dry, of a dark grey
or bluish colour, but weathering to a drab or light grey to a depth
of some feet, in which weathered part a majority of the sections of
course occur. It varies according to the nature of the rocks in its
immediate neighbourhood, and \\k base, which in section is always
clearly defined, is sometimes of a sandy nature, while occasionally
it consists of a hard bed or thin band of crystalline siliceous lime-
stone. The probable origin of this bed has been discussed in the
Memoir on Sheet 47 (p. 60).

The clay encloses many lumps of hard or hardened chalk, more
or less rolled, and frequently striated, but its mass often resembles
in composition the rock on which it rests. North of St Ives the
clay could scarcely be distinguished, but for its boulders, from
Oxford Clay ; near Bourn it resembles Gault, and in the neigh-
bourhood of Balsham it is like, and indeed mainly consists of,
reconstructed chalk. Boulders of other rocks are scattered indis-
criminately throughout it ; they are of all sizes and of many kinds-
Carboniferous Limestone, sometimes polished and grooved, sand-
stones of like age. Oolitic limestones, quartzites, gneiss, mica-schist,
and quartz, fragments of igneous rocks not being uncommon.

Thin lenticular beds of sand, loam, or gravel are sometimes seen
within the mass of the Boulder Clay, but the only certain observed
instances in this area are a bed of loam in the railway cutting W.
of Newnham Hall, between Ashdon and Bartlow, which appears
to occupy that position, and a thin band of laminated loam near
the top of Barrington Hill.

As there are many sections, such as pits, ponds, road and railway
cuttings, in which the Boulder Clay is exposed, and as they vary
but little (except on different formations), they will not be described
in detail. In the following list are named some of the more im-
portant exposures, notes being given of those only which present
some feature worthy of remark.

Pits, <5'C. Westwards from the Line of Section,

Road-cutting half a mile east of Babraham ; 5 or 6 feet of coarse gravel
with lar^e boulders is here seen partially overlaid by greyish white clay full of
chalk pebbles.

Railway-cutting, 6 furlongs E.S.E. of Babraham, shows sandy and
chalky Boulder Clay, with many large stones and boulders of various igneous
and sedimentary rocks. Among these fragments, of the Lincolnshire Oolites
were recognisea. The deposit is 6 or 6 feet thick, and rests on disturbed
Chalk.

Cutting on road from Linton, near the top of Barrington Hill.

Two pits just N.E. of Abington Park, in one of which the clay is seen resting
on the Chalk.

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GLACIAL DRIFT. 75

Railway cutting between Aslidon and Bartiow.

Pit N. W . of the villaf^e of Hadstock.

Chalk pit just north of Little Chishall Church, with the " hard-bed " at the
base of the clay (see Memoir on Sheet 47, p. 60).

Chalk pit at Smyth's End {Ibid., p. 7).

Chalk pit by Newsell's Bury (N. of Barkway) (Ibid., p. 8).

Chalk pit 2 miles south of Royston (N. of Reed) {Ibid,, p. 8).

ITie clay is also shown by a slip on west side of road just opposite the latter
pit, where it yielded several " coprolites *' from the ** Cambridge Greensand,"
which bed occurs at a level of 300 or 400 feet below, this point being near the
summit, whilst the coprolite bed is at the base of the Chalk escarpment.

Fit by the road side, half a mile west of Tharfield.

Pond in small outlier, li miles south of Royston.

Road cutting in small outlier, three quarters of a mile south of Royston.

Drain (probably now filled up) in small outlier, IJ miles N.E. of Royston.

Pits, Sfc, Eastwards from the Line of Section,

Railway cutting two miles east of Bartiow. This must at one time have pre-
sented a fine exposure 50 or 60 feet in depth. The slopes are now covered by
grass, but here and there some fine smoothed and striated boulders protrude.

Pits and ponds in the village of Balsham.

Road cutting between West Wratting and Wratting Grange, where the
junction with the Chalk is shown.

Railway cutting west of Dullingham station. Shows Boulder Clay and
Chalk, with the "hard bed " between.

Sections in the Separate Mass on the Western Side of the Districts

Old quarry south of Haslingfield ; Boulder Clay on Chalk.

Barrington Clunch Pit (see p. 53).

Pit by roadside north of Orwell (see p. 53).

Eversden Quarry (see p. 53).

Road cutting north of Arrington. Boulder Clay on Chalk.

Railway cuttings [S.E. of Bourne, Good sections of the clay, which here
rests on Gault; and, but for its included boulders and chalk fragments,
greatly resembles Gault in general appearance.

Hardwick ; large ponds.

Madingley Clunch Fit (see 41).

Parish ponds at Lolworth and at Boxworth.

The small outlier between Long Stanton and Over is cut off at its southern
end by the railway ; the section shows several feet of gravelly Boulder Clay
resting irregularly on Oxford Clay. There are here some large ice-marked
boulders, two about 3x3x2 feet. *

North of the Otise River.

Railway cutting S.W. of Bluntisham. Shows a scoop of gravelly Boulder
Clay at its east end, a continuation, at a much lower level, of that which
caps the ridge to the west.

The Boulder Clay north of St. Ives is so like the Oxford Clay on which it
rests that it is difficult to distinguish between them, except in good sections.

In the large railway cutting between St. Ives and Somersham the Boulder
Clay is a bluish-grey clay (perhaps rather lighter in colour than Oxford Clay),
enclosing boulders of chalk, flint, and other rocks. The ridge is capped by
this clay with considerable regularity, and on it are scattered patches (seme
being mere remnants) of gravel at a considerable height, certainly not less
than 100 feet above the fen lands.

It will be well to note here the varying heights at which the
Boulder Clay rests on the older formations, and see if these ap-
parendy irregular variations have any definite relation to each
other; and if so what conclusions may be drawn from them.

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76 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

Taking first the edge of the main body of the clay, where it
winds along the summit of the Chalk escarpment, we find that
east of Tharfield its base is about 530 feet above the sea ; this
height (and the remark applies to all which follow) being an ap-
proximation to the truth ; few Ordnance levels are given in the
district, some of the heights have been taken by aneroid, and in
other cases allowance has to be made for the estimated thickness of
the deposits ; but any error there may be is too small to greatly
affect the general question. The surface on which the clay
rests falls slowly, almost imperceptibly, eastwards until it crosses
the section line at Barrington Hill at a height of 300 feet. It
is the same at the windmill west of Horseheath, but it rises
again in the direction of Balsham, where it would be about 350
feet, whence it again i'alls slowly in the direction of DuUingham,
beiug about 240 feet E. of Newmarket, and the depression is
probably continued further.

For the present this may be considered as an even line (with
occasional local depressions, tne base of the clay quickly returning
to its normal elevation), not level, but sloping gradually to the
north-east in the direction of the Chalk escarpment. The fall is
180 feet in 18 miles, or only 10 feet in a mile, a proportionate
incline of 1 in 528, equal to an angle of little more than 0° 6'.

But we find the clay more rapidly descending, from the 'scarp,
in a generally transverse direction, probably to south and east
as well as to north and west ; but with the latter only are we
at present concerned. Starting from the highest point (530 feet)
by Tharfield, and going in the direction of Cambridge, we cross
three small outliers of Boulder Clay at successively lower eleva-
tions, the distances apart and the relative levels being as follows : —

Successive
Distances.

Fall in Feet.

Angle.

Proportionate
Licline.

1 mile - - -
i ,, -
1J„ -

80
80
15

Nearly 1°

1«>

0<^6'

1 in 66.

1 in 57.

1 in 600.

These data give a uniclinal curve corresponding with the form
of the old surface on which the clay was deposited, its steepest
part, about IJ miles from the present scarp line, being inclined rather
more than a degree (see Fig. 14, p. 77).

Again, at Barrington Hill the base of the clay is 300 feet above
the sea, and it descends thence by Hildersham and A bington nearly
to the bottom of the valley at Babraham.

Dis-
tances.

Fall in
IVet.

Angle.

Propor-
tionate
Incline.

From the S.E. to the N.W. boundary of the
patch on Barrington Hill - - -

From the N.W. boundary to the bace of
patch at Babraham - - -

1 J miles

15.5
60

1° 9'
0^ 1.5'

I in 50
I in 220

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GLACIAL DRIFT.

It is soen here also that the sharpest slope is somewhat in advance
of the escarpment. The general slope of the base of the clay is
obtained from the following data, referring to a line drawn through
the outliers of the first table, in a direction nearly north across the
Orwell Ridge, and through the small outlier between Long Stanton
and Over to another ridge north of St. Ives.

Succes-
sive Dis-
tances.

Fall in
Feet.

Angle.

Propor-
tionate
Incline.

No. 1 Ontlier

No.2 „

Onvell Maypole - - - -

Dry Drayton (boandary) - - -

Outlier between Long Stanton and Over -

1 mile

4 „

SO-
SO-
145-
105*
70-

Nearly 1°

0° 13'
0° 10'
0° 11'

I in 66
lin57
1 in 264
1 in 330
1 in 300

From this last point to another south of Bluntisham, 3i miles
across the Ouse valley, a line joining the base of the clay at the
two places would be nearly level ; it then rises at least 30 feet in
half a mile to the summit of the ridge, that is at an angle of 36',
equal to a proportionate incline of not less than 1 in 88. A small
outlying patch of the clay at Burleigh Hill Farm, somewhat off the
line, but still between St. Ives and the ridge to the north, occupies
ground at an intermediate level, thus conforming to the general
lie of the base of the clay as determined by a consideration of the
various levels.

It will be seen from the above that the small outlier between
Stanton and Over, now a mere remnant, occupies the lowest point,
or thereabouts, from which the base of the clay rises in each direc-
tion. This rise is not great, but it is constant, and for the area in
which it occurs appreciable ; we are not dealing with a hilly dis-
trict, a fact which makes observations of this kind the more diffi-
cult, but none the less valuable or suggestive. The diagram.
Fig. 14, has been constructed from the above data, and shows the
original base of the clay along the line described, which may be
taken to represent generally the contour of the surface from the
escarpment to the fens at the time of the deposition of the Boulder
Clay.*

Figure 14. — Diagram Section showing the slope of the Boulder Clay.

The dotted line shows the present surface.

The line a a shows the original base of the Boulder Clay ; * ♦ Sea-level.

From the form of the old surface on which the Boulder Clay rests,
determined by these heights and the lines connecting them, we learn

* See also. Physical Geology of East Anglia during the Glacial Period. W. H.
PawNiNa, Quart, Jour, GeoL Soc,, vol, xxxii. p. 198.

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78 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBRIDGE.

that the Cambridge Valley, as such, is Pre-glacial, or at all events
that it existed very much in its present form before the Boulder
Clay was deposited. The main line of drainage was, as now, that of
the Ouse, a fact primarily owing to the more rapid erosion of the
beds along the anticlinal line, as previously suggested (p. 6).

It is not asserted that the clay rests on a perfectly even surface ;
it is indeed locally uneven, but its general slope is as indicated, the
accuracy of the Ime between the selected points being borne out by
intermediate heights and by the manner in which the boundary
follows the contour. There are many slight hollows or channels,
and wherever the clay runs out in a narrow tongue it may safely
be assumed to occupy such a hollow ; examples occur east of
Conington, at Dry Drayton, and at Comberton, while a more
striking instance is the long narrow strip which caps the ridge of
the Orwell Chalk outlier.

There are other and still more important channels in the old
surface under consideration ; one is partly along a small valley
which runs from near Balsham to Hildersham, and is partly shown
in the section, Plate 6.

Three miles south from Barrington Hill along this section line
we find the clay only 160 feet above the sea, and at Babraham it is
only 106. Between these points, that is east of Abington, its base
is about 120 feet, and the patch of Boulder Clay at this place
rests not on a level surface, but against the flank of the chalk hill.
The position on the slope, and at a lower level than the main spread
of clay, together with the gradual fall in one direction, bears testi-
mony to the fact of the scarp at this point having been cut through
by an old valley, nearly along the present line of the Bourn River,
which was filled by Boulder Clay and has since been re-excavated.

A similar set of circumstances occurs about Chesterford ; a de-
pression in the normal base line of the clay along the escarpment,
and some small patches of clay in the valley, inmcating the exist-
ence of an old valley through the escarpment These are the only
two cases within the district, and the conclusions derived from
them are in both instances borne out in a remarkable manner by
additional and similar evidence. In the valley along the line of
section (Plate 6) a thin bed of gravel occurs beneath the Boulder
Clay (see p. 73) ; and a little lurther north by Bartlow is another

Eatch of gravel, hitherto considered of doubtml age, which on this
ypothesis might be older than the Boulder Clay. In the Chester-
ford Valley is a bed of loam contorted and devoid of fossils,
possibly passing in under Boulder Clay, and perhaps referable to
the same period as the above. The large patch of gravel south of
Whittlesford rests on a chalk slope, thinning out against the higher
ground, and is probably of the same age as the Chesterford loam«
Both this gravel and that at Bartlow present lines of bedding which
dip at a high angle, both are unfossiliferous, and resemble some-
what in these and other respects the known ** Middle Glacial"
beds on the south of the Chalk range. The presence within this
area of gravels differing from all the others may be due to an ex-
tension of the southern gravels along the lines of the old valleys^
where they would form a basement bed to the Boulder Clay.

On the other hand, in the absence of evidence from super-
position, it is possible that these three patches at Bartlow, Chester-

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GLACIAL DRIFT. 79

ford, and Whittlesford may be newer than the Boulder Clay, and
belong to the old river series hereafter described (p. 85).

Marine Geavels and Loam.

This series, which is of late Glacial or very early Post-glacial
age, occurs in sraall patches, single or in groups, of loam containing
stones of various sizes and description, or of loamy gravel. The
loam is not often good enough or in sufficient quantity to be useful
for brickmaking, although some pits in it are worked for that
purpose, neither is the gravel of good quality, requiring to be sifted
and sorted to render it available for road-mending.

These remnants of what must formerly have been an extensive,
if a thin, deposit generally occur in lines, and thus seem to have
some definite relation to each other. They occur generally on the
table lands and higher grounds, and probably occupy old depres-
sions or channels in the rock beneath, having thus been some-
what preserved from denudation.

The section (Plate 6) traverses a line of these patches of
gravel, commencing on one of them at Ashdon. From this poinit
they rise gradually to the top of Barrington Hill, then fall towards
the old line of valley previously described (p. 78) to their lowest
point E. of Babraham — ^resting on Boulder Clay with one partial
exception. From this spot they lie on the Chalk, and rise gra-
dually to the summit of the Grog- Magog Hills at Vandlebury.

It is but right to state that our colleague Mr. Whitakek,
who has seen these gravels with us, does not altogether agree with
our classification. He writes to us : "I think that some of these
gravels may be older than the Boulder Clay, rather than of late
Glacial or of Post-glacial age, for the clay that sometimes occurs
in thin patches on them seems to me to be Boulder Clay weathered
in place, and not reconstructed, being exactly like what results
from such weathering in other districts. For instance, in the
pits on the northern side of the road a quarter of a mile "W.S.W. of
Bishop's Charity Farm, on the hill southwards of Cherry Hinton,
there is what seems to me to be weathered sandy Boulder Clay
above the gravel."

The pits at Asbdon are in rdugh chalky gravel, false bedded, and in one
case with a black band (? manganese peroxide) at the bottom, from 6 to 8 feet
being shown.

Barrington Hill is covered by Boulder Clay, which towards the top includes
a thin bed of laminated loam, shown in the road cutting about three-quarters
of the way up the hill from Linton. The hill is capped by coarse brown
gravel (as seen in a pit 6 feet deep in 1874, but since filled in) with large
stones and some quartz-pebbles. Other patches to the W. and N. occur at a
lower level. The Boulder Clay forms almost an outlier, being united to the
main spread only by a narrow neck on the eastern side.

In'the patch to the north the junction of gravel over the clay was obtained by
digging m the slope of the road cutting about a furlong N.E. of the small
ChSk inlier exposed by denudation of the Boulder Clay.

There is a spring at the N. end of the large patch of gravel E. of Hil-
dersham, the water of which is thrown out by the clay, in an hollow on the
surface of which the gravel rests. Beyond this the gravel overlaps the Boulder
Clay and rests on the Chalk, the junction being exposed in the cutting at the
cross roads. There is an old gravel or sand pit just N. of the "I" in
** Hildersham,** but the section is now overgrown, and at the W. end of the
patch is an old " Sand Pit/' also overgrown, marked on the Ordnance map.

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80 GEOLOGY OF THE NEIGnBOURHOOD OF CAMBBIDGE.

By the junction of roads a quarter of a mile N. of Hildersham Churcli
there is an exposure of 10 feet of stiff grey Boulder Clay^ with a lenticular
patch of sandy loam at the bottom, and on the top a pocket of sandy grtLvel,
probable once connected with that which now caps the hill above.

At Clay-pit Plantation the gravel appears to lie above the Boulder Clay, but
the section is completely grown over. The Gravel pit on the hill, a quarter of
a mile N. (on the Une of section), showed 8 feet of compact angular flint gravel,
stained dark brown, and with a thin interbedded band of brown sand. The
road-cutting 3 furlongs S.W. is in sand, with flints and chalky grave] in very
confused beds to a depth of 7 or 8 feet, and there is an old gravel pit in the
plantation near by.

The pit a quarter of a mile N.W. of Little Abington Grange is in coarse
confused gravel, mainly composed of large flints and chalk pebbles set at all
angles, Cambridge coprolites, and red chalk, with pieces of septaria, quartzites,
and other rocks.

The cutting on the Newmarket Road, by the 50th milestone from London,
just W. of the above section, shows Boulder Clay capped by about 2 feet of
coarse gravel, consisting of stones derived from tne Boulder Clay impacted in
a reddish sandy clay.

Signal Hill, to the N.W. of the above, is apparently capped by gravel, but
no section was seen. On the hill to the nortnward, however, gravel is again
found, though the pits two furlongs N.W. of Worsted Lodge are partly
grown over ; a new excavation showed 6 feet of gravel, consisting of chalk
stones, stained yellow outside and packed close together, with hardly 5 per
cent, of other stones ; the top 2 feet had, however, some flints in a more sandy
matrix. Another hole showed the following deposits : —

Feet.
Irregularly bedded sand and gravel • - - 3

Very chalky gravel - - - - • - 3

Grey sand - - - - - - - 1

The other end of this outlier had also been excavated, and the gravel there
apparently contained more flints.

The gravel pits N. of Fulboum Lodge gave the section below : —

Sand and chalky gravel under the edge near the entrance, passing
towards the top of the hill into 3 feet of chalk-rubble and sandy clay,
6-8 feet.

Bedded white chalk, 10-12 feet.

A small pit at the £. end of the same outlier showed a foot of yellow lami-
nated loam over 2 feet of fine gravel, consisting of chalk and flint pebbles.

Copley Hill, Misleton Hill, and Little Trees Hill are capped by similar
gravel.

The old pits, half a mile W. of Hill's Farm, are well known, and have been
described by Prof. Sedgwick and other geologists. The beds exposed here
in 1875 were as follows : —

Stiff jrellowish sandy clay, containing stones of various sizes and set at
vanous inclinations ; the pebbles of chalk are rounded, the others
angular. About 50 per cent, are chalk, 30 per cent, flints, and 20 per
cent, of various other rocks, 6 feet.

Coarse rubbly gravel, said to have been obtained Arom below this, and
resting on Chalk, 3 to 4 feet.

On Steeple Hill, north of Shelford, there is a patch too small to be
mapped, being merely a pocket of coarse gravel at the top of the clunch pits.
This is probably the bottom of a long pipe that descended through beds of
chalk since removed by denudation, and thus is far below the level at which
the base of these gravels once extended over this ground, being nearly 100 feet
lower than the summit of the Gog-Magog Hills.

There are other patches of similar gravels to the N. and £. of the section
line, resting on remnants of a surface gradually sloping from the highest points
of the escarpment down towards Newmarket. An elevated spot £. of Balsham
is covered by a thin patch of gravel, in which were no sections. Between this
and Barrington Hill a tiny patch remains, and there are traces of another just
S.W. of West Wratting.

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GLACIAL DRIFT. 81

A mile S.E. of Westley Waterless, and on high ground, is a patch of loam
only a few feet thick, and thinning out all round to a mere loamy soil. It is
exposed in a brickyard at Brinkley near its southern end ; at the northern end
also is an old brickyard.

Many patches of Gravel on the Chalk ridges are too small to be mapped;
they make no feature, being in old channels, and can be seen only when cut
through.

There is a small patch of loam on the Boulder Clay, on the top of the escarp-
ment £. of Tharfield, about 500 feet above the sea ; it may be seen in section
at the brickyard. (See Memoir on Sheet 47, p. 64.)

A small patch of yellow gravel, li to 2 feet thick, occurs on the higher part
of the Boulder Clay at Elsworth Common, about 8 miles westward of Cam-
bridge ; it contains large pieces of a siliceous rock which is found also in the
upper part of the Boulder Clay.

A similar series of gravels to that on the Barrington and Gog-Magog Hills
caps the ridge of Boulder Clay, which rises to N.W. of the Ouse vaJley from
Bluntisbam. The spring haJf a mile W. of that village is thrown out by the
Boulder Clay beneath a chalky gravel ; there is a small pit in this gravel S.E.
of the mill, and another in the small patch to the E. The Httle patch
half a mile W. is not now seen in section ; indeed, it seems to have been nearly
all dug over and carried away.

A quarter of a mile N. of the mill is a small pit in the larger patch
showing about 3 feet of rolled chalky gravel and Oohtic d^ris ; this is again
seen in section a few chains to the north. Along the top of the ridge to the
W. are many small unmappable patches of gravel and gravelly soil; and at
Wood Hurst is a long narrow strip of gravel and yellow loam seen only in
one section, but giving ample evidence of its existence and extent.

Another spur of this higher range of the Boulder Clay, a mile S.E. of Pidley,
is flanked and just overlapped by a small patch of gravel and eand. There
were gravel pits here at some time, but they have been long abandoned, and
no section is visible. A minute patch of gravel or sand still remains on the
summit of an elevation S. of Somersham, and about Warboys, on the high
ground in the N.W. comer of the map (Plate 7), are patches of gravel, now
so thin, however, that they might more properly be called a gravelly soil.

The above sections show that this series of gravels consists
of materials such as would have been derived from the waste
of Boulder Clay — chalk, flints, oolites, and boulders of rocks of
many kinds. It will be observed also that in many of the pits the
chalk pebbles are seen to be rounded, while those of other rocks
are frequently sub-angular ; but the quartzites and similar stones
derived from a long distance are generally waterworn.

N309.

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82 GEOLOGY OF THE NEIGHBOUBHOOD OF CAMBRIDGE.

CHAPTER VIII.— POST-GLACIAL DRIFT.

Geavels of the Ancient River System.

The valleys which run northwards and north-westwards from
the chalk escarpment contain some very interesting relics of early
river deposits, which remained unnoticed and undescribed until we
commenced our survey of the district In 1861 Prof, Sedgwick
commented on the supposed absence of such beds from the higher
coombs and hollows of the Chalk escarpment, coming to the con-
clusion that these valleys had been swept out by the action of
** rapidly descending water floods," rather than** by a long con-
tinued and slow process of erosion." If Prof. Sedgwick had known
of the existence of beds of gravel in such valleys he would pro-
bably have been the first to modify his opinion, as he was the first
to reduce the drift deposits of Cambridgeshire into something like
order.

Such patches of these gravels as afterwards became known were
probably regarded as forming part of the series last described ; it is
indeed even now very difficult to separate the higher portions of
these old river gravels from those of earlier date, the two being
much alike in character and composition. The latter, however,
generally occur as outliers on the higher ground, and though they
occasionally descend into hollows they do not appear to conform
in any way to the direction of the old or present valleys.

On the other hand these early river gravels are elongated in the
direction of the long but now dry valleys which run from the Chalk
Hills, and they are found at intervals along the sides of those
valleys, so as to present series which descend gradually to lower
levels. The patches, moreover, are larger at lower levels, and those
from several valleys tend to concentrate at the points of junction,
so that at last thev stream out to form long-continued gravel-
capped ridges which trend more or less in the direction of Cam-
bridge.

It was only after they had nearly all been mapped that the true
character of these ancient river deposits came to be understood,
and in 1875 one of us showed that they might be referred ''to
the existence of an ancient river running, as does the present one,
along the foot of the escarpment, although, of course, not on the
ground occupied by the Cam of our own time. Reasons were
given for this conclusion, and for the proposition that " we have here
a series of river gravel terraces occuring at all heights, from nearly
the bottom of the present valley up almost to the top of the Chalk
escarpment."*

THe great age of these gravels is shown by their general relations
to the principal features of the country ; they are not only for the
most part at a distance from the present river, but their lines of

* W. H. Penning, Quart. Joum. Geol Soc, vol. xxxii. p. 200 (1876). See also
" The Post-Tertiary Deposits of Cambridgeshire," by A. J. Jukes-Bbowne, Cam-
bridge, 1878, p. 46.

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POST-GLACIAL DRIFT. 83

direction are different from, and sometimes transverse to those of
the latter. Tliey fill old channels, which must have been low
ground when these gravels were deposited, though now often the
highest in the neighbourhood. Their fluviatile origin is proved by
their connexion with the upland valleys, and by the occasional
occurrence of land and fresh water shells and mammalian remains.
The most westerly series of these gravels begins in Wardington
Bottom, a deep coomb-like valley described as having received its
initial form and its commencement from the flexure in the Chalk
S. of Royston (see p. 67). It is bounded on the S. and E. by the
highest part of the Chalk escarpment, on the W. and N.W. by elevated
ridges, here and there capped by patches, as the scarp is by the
mass, of the Boulder Clay. Its sides are steep, and descend in a
distance of about a mile at least 300 feet, and it forms altogether an
amphitheatre of Chalk, into which project descending and converg-
ing tongues, with minor coombs between. But it is virtually a dry
valley, the small channels that occupy the bottom being without
water for a greater part of the year.

Half a mile west of the " W " in " Wardington " is a small patch of the
gravel, which occupies the high ground between two small channels that unite
just below. A large patch remains S. of Knowns Folly, and a wash from this
extends down to the low ground, and between the gravel and the wash there
is no definite line of division. A minute patch occurs on the higher ground
half a mils east, and North Hall stands on a much larger one.

Some notes of the pits in these outliers have been given in the memoir on
sheet 47, p. 71, but the localities have since been revisited and additional
information obtained.

At North Hall the pit near the house is about 9 feet deep in chalky gravel
with seams of sand, and boulders of quartzite, basalt and other rocks. A
newer excavation by the roadside east of the farm shows a similar section, and
the workmen said large bones were often found.

At the pit north of Sharpens the following section was seen in 1878 : —

Feet.
Fine chalky gravel - - - - - 2

Brown laminated loam - - - - - 1

Gravel of small flint and chalk pebbles, with occasional
layers of fine sand - - - - - 6

In another place the layers were bent down so as to dip northwards at an
angle of about 20°.

These patches of gravel are on ground considerably above the present water-
course, and gradually leave its direction, that at Sharpens being half a mile
away ; another patch N.E. of Heydon Grange, in which no pit occurs, is at
the same level and at a still greater distance. The ground to the N. and N.E.
of this is covered with a sandy and flinty soil, which leads on to a large out-
spread of gravel and sand; this is important from its size relatively to
the others, from its forming a distinct and prominent ridge in the midst of a
Chalk plain, from its continuing its direction, while the existing stream bends
away at right angles, and from its yielding remains which testify to the mode of
its formation. It extends for upwards of 2 miles from the road N.W. of
Chrishall Grange in a N.N.E. direction by Crowley Hills to a point S.E. of
Triplow. It is about half a mile broad ; but its southern half consists
mainly of sand, and its boundary at that part cannot be accurateljr defined,
for the sand has come down over the Chalk slope in every direction, giving rise
to a sandy soil greatly resembling that on the sand itself, and sections (even in
ditches) are entirely wanting.

The northern end of this long ridge consists of gravel, and is much more
clearly defined, although it also gives rise to a sandy soil on its western side.
It may be noted here that under certain circumstances, for instance in the
summer season when the ground is covered with crops, it is almost impossible to
say where these gravels actujJly end. Both the Gravels and the Chalk on which

F 2

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84 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

they rest are so highly absorbent of moisture that ditches are needless, ponds
are useless, draining is not required ; therefore when no pits occur one has to
depend for evidence upon surface indication. The gravels cap the ridges, and
of course the material of which they are composed, works down the slopes, and
overlaps the actual boundary.

Although this patch of gravel now forms an elevated ridge throughout, it
doubtless occupies an old hollow in the Chalk, trending N.E. in the direction of
Whittlesford. The base of the gravel is not level at its northern end, the
boundary on the Triplow side being much higher than that on the other,
showing that this part is banked against a sloping surface, or rather occupies a
hollow in the sloping surface of the chalk.

A pit W. of the track from the high road to Duzford Grange gave this
section : —

Coarse Chalky ^vel, roughly stratified, nearly all flints, not
much rolled, with a small intercalated patch of loam contain-
ing shells — Stuidnea Pupa, &c. - - - - 8 feet.

Fine chalkjr sand - - - - - - 1 foot.

Gravel entu^ely composed of small chalk stones - - - 1 foot. \

Fine sand.

There is a smaller patch of similar sand E. of the Grange, which from its
direction seems to indicate the incoming at this point of another line of gravels,
of which this is the only remnant. The sandy or loamy nature of the deposit
in this patch, and at the southern end of the large one, would also seen to bear
out the idea of a junction of streams at this point.

Another patch of gravel is seen on the E. side of the main one, from which
it is separated by a narrow band of Chalk, exposed by denudation along the
lower ^ound occupied by the road N. from Chrishall Grange. A pit at the
N. end shows a foot of sand over 2 feet of chalky gravel resting on Chalk.

About a mile north-east another large patch of gravel and loam commences,
and is a mile and quarter long and three-quarters of a mile wide. This also
rests on a sloping surface of chalk, the boundary of its western end being on
high ground, that of its eastern side 20 to 30 feet lower, in the valley by
Whittlesford Railway Station. There is, as before stated (p. 79), some doubt
about the age of part of this gravel; but we believe that whether the
gravel at its southern end be of Glacial date or not, some of it belongs to the
ancient river series. The gravel as seen in two pits west of the station is much
contorted, still we think this feature quite compatible with the conditions under
which the ancient river series was formed (see p. 123). It will be seen that
in the pit noted below, and shown in Fig. 15, a pre-existing bed of gravel has
been scooped out, and the part so excavated afterwards occupied by loam,
gravel again coming on above. We consider that the loam and the overlying
gravel are a part of the series now imder consideration.

Fig, 15 — .Section in the Gravel Pit on the south side of road a few
chmns west of Whittlesford Railway Station,

Scale, 16 feet to an inch.

g. Gravel -.---. 2ifeet.

f. Fine light-coloured sandy loam - - - 12 „

e. Gravel and sand - - - - -"|

d. False-bedded sand - - - - -vxic

c. Gravel ^about 15 „

h. False-bedded sand - - - - -J

a. Gravel, excavated to a depth of - - - 7 w

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POST-GLACIAL DRIFT. 85

A few yards nearer the station than the part shown in the figure is a small
cave, scooped in gravel ; the roof of which is formed by the under-surface of
a loam (probably ==f.) dipping north about 15°.

A gravel pit just S.W. was about 10 feet deep in gravel, with contorted loam
and layers of sand.

At the brick yard, on the north side of road, about a third of a mile west
of the railway station, the pit is in finely laminated sandy loam, grey at the
bottom, weathered buff towards the top ; dug to a depth of 20 feet, from the
lower part a broken specimen of Cardium edule was taken.

A pit, half a mile N.W. of the railway station, showed 20 feet of coarse
roughly stratified gravel cut off on the south by a grey sandy loam, probably
the northern edge of the same bed as that seen in the brickyard, and in the
gravel pit. Fig. 15, where the loam cuts out the gravel in a similar manner.

The gravel just S.W. of Bartlow, which is of doubtful age (see
p. 78), seems to us to be referable to these ancient river gravels.
For details see Memoir on Sheet 47, p. 72. Between this and
Whittlesford are several other patcjies at about the same level,
and these we conceive to be remnants of the same series, repre-
senting an old river-line from Ashdon by Bartlow, Linton, and
Pampisford Hall, joining thait from Wardington Bottom at or near
Whittlesford. The united streams turned thence northwards,
and although no more traces of similar deposits are now found it
is owing to the fact that no ground high enough to reach their
level remains on this side of Cambridge ; the old line must have
passed somewhere through the gap formed by the Gog-Magog
Hills on the one hand and by the Barton and Madingley ridges
on the other. There is a very small patch of gravel stiu remaining
on the top of Redland Hill, near Harston Station, which is pro-
bably the last remaining trace of another tributary of the old river,
but except the ridge itself, which points by Jj^aggots Mount
towards Shelford, there is nothing to indicate its dirt^ction.

Another drainage system appears to have been contemporaneous
with those just described, and to show that the two great streams
thus produced met somewhere in the neighbourhood of Cambridge.
The tributaries of this second river descended from the hill-slopes
about Balsham and Brinkley on the other side of the watershed
formed by the Gog-Magog Hills and the high ground by Abington,
Balsham, and West Wickham. From these high lands several
long dry valleys converge towards the N. and N.W.

The westernmost of these commences south of Balsham, near New Yole
Farm, and trends to the N.W. About half a mile W.S.W. of Balsham lime-
kilns a very small patch of gravel occurs just on the brow of the hill, probably
occupying a hollow in the chalk. A little further down, and on the opposite
side of the valley, some gravel pits have been marked on the map ; these are in
an elongated patch of gravel, sand, and loam, and exhibit a section that is
somewhat peculiar from the rapid thinning out of several beds, and from an
anticlinal curvature along an axis parallel with the direction of the valley (see
Figures 16, 17). The loams and sands show that there must have been quiet
reaches in the rivers by which these beds were formed. The saddle-back was
probably caused by a gradual dissolving or washing away of the chalk on either
side of the gravel, which now occupies a ridge, but must have been on a flat
or in a channel at the time of its deposition. The northern end of the patch
is almost all yellow loam.

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86 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.
Figs. 16, 17. — Sections in Gravel Pit 2 miles W. of Balsham.

m^;

^^^^m.

^ .- * i»'^ --r »'/ /r/ r»i; ■ <

(Scale, 16 feet to an inch.)

h. Soil.

g. Grey loam.

f, False-bedded sand and gravel.

€, White false-bedded sand.

d. Yellow false-bedded sand.

c. „ finely bedded sand.

b. „ sand, false-bedded at bottom.

a. Fine &lse-bedded gravel.

The gravel of the Balsham pits does not occupy the highest ground, but it
rests on the western flank of a deep valley, which runs between two outliers
of Boulder Clay, and its western side abuts against, and partly rests upon,
a smaller patch of that clay.

A space of a mile and half intervenes between this remnant of gravel and
the next in the same series, which occupies the summit of a minor elevation,
just N.W. of Dungate Farm, situated on the line of the Balsham Ditch, where
the pits show 6 or 8 feet of chalky and somewhat clayey gravel, with patches
of sand ; the material is made up apparently of waste from Boulder Clay, and
contains many pebbles of hard and soft chalk, flints, mostly angular, quartzites,
and fragments of other rocks. In places a red-brown sand occurs on^the top,
many of the flints below being deeply stained thereby.

North of this there is a much larger mass which rests partly on the flank
of the hill west of Wratting Valley Farm, the western boundary being at a
higher level than the eastern. Its northern end, however, runs out as a spur,
pointing directly to the south-eastern end of the gravel-ridge near Great
Wilbraham.

The pit by the side of the road, about 1 J miles S.S.E. from Great Wilbraham,
shows 6 to 8 feet of hard chalky sand with scattered flints, but very few chalk
stones ; the upper part is more sandy from the dissolving away of the chalk
grains, leaving the flints embedded in a brown sandy soil. Below are pockets
of light-coloured sand full of flints descending into the Chalk,

A small excavation about a quarter of a mile northward was 8 to 10 feet
deep in coarse flint-gravel, the stones being closely compacted and set in a
ma^ix of chalky sand, most of them having their long axis vertical; a few-
lenticular patches of sand gave a rough appearance of bedding.

The railway cutting shows 6 feet of whitish chalky sand, full of angular
unrolled flint fragments, with the faces of cracked pieces sometimes coated by
Carbonate of Lime, and a few chalk pebbles. Thence the ridge continues in
the direction of Great Wilbraham.

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POST-GLACIAL DRIFT. 87

To the east of the line just described there are two other valleys
which run north-westward from the slopes about West Wratting
and Weston Col ville, in 61 S.E., and both of these contain a similar
series of gravels. As before, they commence with small outlying
patches in the hollow of the present valley, farther down larger
outliers occur high up on its slopes, till eventually they desert the
existing line of drainage and are continued along the ridge which
separates the two vallevs at Six Mile Bottom. This ridge is pro-
longed for upwards of four miles in the direction of Wilbraham and
Quy-cum-Stow, and forms a remarkable feature indicating the
enormous amount of denudation (or as we should prefer to say
detrition and devection of material) which must have taken place
since the deposition of thes'^e gravels. How great must be their
antiquity, when the valley-bottom along which the ancient river
ran is now an elevated ridge from 30 to 40 feet above the ground
on either side.

In the first of the above-mentioned valleys the highest patch is merely a
speck on the map, nearly a mile north of Balsham Church.

For some distance further down the valley all traces of the old gravels seem
to have been, destroyed, but at a point about a quarter of a mile N E. of
Wadley Hall, and on the slope of the spur made by the junction of a tributary
with the main vaUey, there is another patch, too small to be shown on the map ;
it fills a hollow, and here many mammalian bones were obtained, some of
them being now in the Woodwardian Museum at Cambridge. (See list, p. 106.)

On the slope N.W. of Lark's Hall a larger patch of sandy gravel occurs,
from which also bones are said to have been obtained.

Half a mile northward another outlier lies on the flank of a ridge extending
toward the railway, and the end of which appears to be capped by a small
patch of similar material.

In the second valley from Weston Colville, only two or three small patches
of gravel have been found, the first being a narrow capping to the ridge, about
a quarter of a mile S.W. of Carleton Grange, with some old pits, now ploughed
over, several feet in depth. A tiny remnant occurs just N. W., and a sandy soil
in the only sign of a similar deposit on the ridge east of Lark's Hall.

There is a pit in the small patch by the road, a mile S.E. of Six Mile Bottom
Station, which shows 4 feet of gravel, made up almost entirely of flints and
chalk pebbles.

On the opposite side of the valley is a more extensive gravel-covered area,
forming a ridge, the northern end of which is cut through by the railways
a short distance east of Six Mile Bottom Station. A small gravel pit was open
in 1875 in the fields about half a mile east of the station, showing 6 or 8 feet
of gravel and sandy loam.

The railway cutting shows 6 or 8 feet of sandy gravel, the matrix being a
hard compacted yellowish-white sand, in which are scattered flints of all sizes,
many being unrolled and fresh from the Chalk ; no chalk-pebbles, and only
a few brown quartzites. The bottom is obscure, but seems to be in chalk.

This spread was probably formed at the confluence of the two tributary
streams, the course of which we have just been following.

Some other patches of sandy gravel are also found to the northward, by
"Westley Lodge and Six Mile Bottom, which are at a much lower level, and
probably illustrate a later stage in the erosion and formation of the present
valley.

Beyond the railway the high ridge which trends north-west is also capped
by gr&vel, but no sections were seen ; this patch terminates by the " Tumuli '*
east of Great Wilbraham, and Chalk comes to the surface about the cross
roads near by.

Gravel, however, again sets in to the north-west and continues for more than
three miles along the ridge, often with a width of half a mile. Several
pits just above the word " Temple " exhibited about 9 feet of irregularly
bedded gravel and sand, some layers of the former being very coarse and

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88 GEOLOGY OF THE NEIGHBOURHOOD OP OAMBEBOGE.

chiefly composed of flints ; a molar of Equus fossilis wbs obtained here, and the
workman said that bones were frequently found. In the hollow by the wood
on the west there is a small pit exposing 5 or 6 feet of clean fine laminated
sand, with some intermixture of chalky matter, but without any trace of gravel.

We think it probable that this deposit of sand was formed in a back-
water produced by the incoming of the river from the south, the course of
which has been already described and its gravels noted as last seen in the
railway cutting S.£. of Great Wilbraham (see p. 86). This appears to have
been the last tributary of the river which thence flowed onward to the N.W.,
and has left such a remarkable memorial of itself in the long ridge which
extends in that direction.

Fig. 18 is a section across this ridge, showing its relation to the lower
ground on either side.

JFig, 18. — Section from Wilbraham Fen to Bottisham,

S. 30 W. N. 30 E.

Droveways. Road. Road. Stream. Boad.

Horizontal Scale, 2 inches to a mile. Vertical scale, 200 feet to an inch.

a. Newer Gravel. h. Gravel of Old River Series. c. Chalk.

The dotted lines indicate the former outline of the ground at the time of the
formations of the Gravels 6, with the probable edge of the Boulder Clay at x.

The large gravel-pit by the roadside just north of Little Wilbraham Church
was 6 to 8 feet deep in sandy loam over compact chalky sand with flints.
Another hole in the same pit was dug in a hard loamy sand, and in this were
found very small specimens of Succinea, and also a minute Pisidium or Cyclas

Gravel holes some 6 feet deep in a field about a third of a mile north of
Frog End, gave the following section : —

Loamy soil.

Sandy and loamy marl with shells (Succinea putris var. minor. Helix, small

sp.. Pupa marginata.
Coarse flint-gravel in sandy matrix.

Some pits by the side of the road a quarter of a mile N,N.W. are in 8 feet
of gravel with sandy beds and patches ; at the bottom the workmen had
found bones.

Gravel has been obtained from several places south of Quy-cum-Stow, and
one old pit is still distinctly marked near the Church.

Beyond this point the continuity of the ridge is broken by the gap which
the Quy water or Wilbraham river has made in escaping from Wilbraham
Fen, but the ground westward is capped with loam and gravelly soil.

This small patch is cut off by another hollow draining into High Ditch
Lane, but westward by Greenhouse Farm gravel and sand again cover the
high ground, along which the main road runs. The behaviour of the gravel
was clearly seen in a ditch running south from the road near the old turnpike,
gravel being shown bedded up against clunch which forms the southern slope.

Where the road to Fen Ditton branches out from the Newmarket Boad there
is an old gravel pit now planted with trees, which we were informed exhibited
about 10 feet of loam and sand, with a bed of fine gravel at the bottom.
Gravel has also been dug in the fields to the S.W., but it thins out as
the slope falls to the west, and the whole series is cut through by the present
valley of the Cam.

If a line be drawn prolonging the direction of these gravels across the
vaUey it will ^trfke and follow that of the long ridge of Chalk Marl upon
which stood tne Roman town of Camboritum ; on this outlier of Chalk Marl
gravelly soil, with descending pipes of the same material, was noticed when
the fields west of the Almshouses were dug for coprolites.

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POST-GLACIAL DRIFT. 89

A small patch of gT&yel was mapped about half a mile to the N,£. near
a farm^ where a gravel pit showed the following section in 1875 : —

Feet.
Brown gravelly soil - - - - 2

Chalky sand with a few small flints - - 4

FUnt gravel set in a matrix of chalky sand, coarser
near the bottom - - - - 4

This gravel lies in a hollow on another small outlier of Chalk Marl, against
the eastern side of which beds of loam and saiid are banked belonging to a
newer series of river deposits, but probably formed to a great extent out of
the older beds of gravel and sand, and the underlying clunch.

It is worthy of special notice that the gravel of Gravel Hill, on which the
Cambridge Observatory is built, lies banked up against the S.W. side of the
Chalk Marl ridge above-mentioned. This was clearly shown in 1873 by the
workings for coprolites in the fields north of the Observatory. The ground
where the gravel thinned out is about 80 feet above sea level, out in the large
pits near the farm, the base of the ^vel is about 18 or 20 feet lower.

A large gravel pit near Gravel Hill Farm, now grown over, gave the follow-
ing section in 18/5 : —

Feet.
Gravel interrupted and disturbed by pockets filled with contorted
brown sand and occasional flints, with films of carbonate of lime
lining the bottom. This is probably due to the dissolving away
of the numerous chalk pebbles - - - - - 6

Fine gravel, rather irregularly bedded, consisting of nearly 50 per
cent, of chalk pebbles, the rest flint, with a few hornstones,
quartzites, &c., one large boulder evidently derived from the
neighbouring Boulder Clay - - - - - 6

Professor Sebley states that he found shells '*' in the gravel under the Obser-
vatory,"* and there is a flint flake in the Woodwardian Museum which is said
to have been found in gravel near this place.f

We have here a repetition of the phenomena noted near Great Wilbraham,
where we concluded that a tributary from the south entered the main river,
and we think, therefore, that there are strong grounds for supposing this to
be the point where the great stream from the southern valleys joined its current
to that coming from the east. It will be remembered that we could not follow
the course of the former much beyond Whittlesford and the ridge by Stanmoor
Hall, but that we supposed it to have been continued in a northerly direction,
which would naturally bring it near the point we have indicated as being
thejunction of these two early Post-glacial rivers.

The stream from the south was, moreover, likely to be the more powerful,
from its greater length and wider basin of drainage. We should therefore
expect that its current would prevail over that of the more easterly stream, and
give a northerly direction to the river which resulted from their union. This
18 precisely what appears to have happened, for a long ridge thickl)r capped
with gravel extends from this point in a direction N.N.W. towards Girton, so
that the watercourse which we have been following from the east was here
deflected northwards after its junction with what perhaps may be considered to
have been the main river.

It is of course very difficult to point out the exact place of junction, but
from the relations of the Observatory and Castle End gravels to the inter-
mediate chalk ridge we are inclined to think that it was a little farther north,
probably in the neighbourhood of How House, where the gravels seem to
occupy channels in the Gault, having a general E.S.E. direction.

At Bunkers Hill Farm, opposite the branch road leading to Girton, the well
is 8 or 10 feet deep in gravel, and a small excavation behind the houses exposed
a few feet of hard compacted yellowish- white gravel, composed mainly of chalk
pebbles and small flint stones.

* Quart. Joum. Geol. Soc, vol. xxii. p. 475.
t Evans* " Stone Implements," p. 485 (1872).

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90 GEOLOGY OP THE NEIGHBOUBHOOD OF CAMBRIDGE.

Girton College stands on some thickness of gravely for a well was sunk
10 feet deep in gravel and sand without reaching Gault^ and in old gravel pits
near the road, where 3 or 4 feet of brown sandy gravel may be seen.

A little distance north of the College the gravel ridge seems to be worn
through down to the Gault, but this latter cannot be exposed over a width of
more than 50 or 60 feet, as gravel is again seen in the lane to the northward,
and it occupies a considerable area about Girton. Sand and gravel have been
dug in several places north of the church (there is 8 feet of it at Mr. Battison's
farm), and in a small outlying patch near the rectory 8 or 10 feet of clean white
sand was seen banked up against fine yellow gravel.

North of Girton the ground falls again, and Gault is exposed for a little
distance, but at the farmstead, about a quarter of a mile from the railway,
gravel was again found (about 7 feet deep in the weU). Thence a gravel flat
extends across the railway to Histon, sloping eastward towards the newer
gravels which are here banked up against the older ridge, and ending west-
n'ards along a well-marked terrace-like line produced by the action of springs,
which are thrown out at its base and drain into the brook that runs to
Oakington.

At the cottage by the level crossing over the railroad between Histon and
Oakington the well is 13 feet deep, with a bottom of silvery sand, and close by
are some large ballast pits now filled with water. From this the ridge trends
to the N.W. towards Oakington, and the little brook which flows in that
direction from Histon has cut through and re-arranged the older deposits.

There are two outliers on the N. bank of this stream which appear to be
remnants of the higher series, and old gravel pits are to be seen in one of these,
which caps the high ground N.W, of Histon church.

Continuing the N.W. trend a mass of gravel almost joins that west of
Histon, is nearly three miles long, and forms the ridge which for more than a
mile is occupied by the village of Long Stanton.

A small pit a quarter of a mile S.E. of Oakington Church showed a foot of
brown stratified gravel on fine yellow gravel 2 feet thick, with white sand
below.

Another pit just N.E. of the church gave the following succession : — Sandy
wash, 2 feet ; fine yellow stratified gravel, 4 feet ; light-coloured sand, 3 feet.

Another pit a furlong N.E. of the church gave a section of similar stratified
beds, as follows : —

Feet.
Gravelly wash - - - - - 3

Fine chalky gravel - - - - - 2

Fine chalky iron-stained gravel - - - 3

Light-coloured sand.

Professor Seeley has recorded the fact that he " found shells in the gravel
"... at Oakington, but in every case they were land or freshwater forms,"*
which confirms our conclusion that this line of deposits is of fresh water origin,
and a continuation of those traced from the neighbourhood of Balsham and
Wilbraham, in which similar shells have been here and there discovered.

The upper part of the ridge by Long Stanton consists of loam, which appears
to have been dug in several places for brickmaking, but no good sections are
now to be seen ; it was, however, exposed in an old excavation N.E. of All
Saints Church, and a strong spring is thrown out at the base of the gravel a
quarter of a mile N. of Oakington station.

Near the boundary of the gravel, half a mile E. of Long Stanton, is a pit
which shows : —

Feet.
Contorted white marl - - - to i

Contorted buff loam - - - J

Fine chalky gravel - - - 2

There are many exposures of this gravel in ponds, and ditches, and in a pit
by " the Cottage " at the northern end of the outlier.

Quart. Jotirn. GeoL Soc, vol. xxii. p. 475.

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POST-GLACIAL DEIFT. 91

On the east side of this large outlier is a small patch of the gravel cut off hy
the stream. In this is a sm^ pit showing 5 feet of fine^ false-hedded chalky
gravel and sand.

It must be observed that this old vaUey gravel here, as elsewhere, occupies
comparatively high ground, and has no reference at all to the existing valleys.
On the strength of this peculiarity we provisionally include in the same series
an elevated patch of gravel on which the village of Over partly stands, but
this, except for its continuity with those described, would seem from its position
to belong to a higher terrace of the Ouse valley deposits.

The patches between Over and Stanton are similarly included, and one of
these, it may be noticed, is still in contact with a paten of Boulder Clay, the
lowest of all in the area described. A pit half a mile S. of Over Church shows
4 feet of angular gravel and sand.

It may be that the larger outlier of gravel on which WiUingham stands
belongs to this series, or, what is more likely, that the small patches on the
west, just noted, and which are of a more chalky and loamy description, are
the only remaining representatives of these ancient river gravels. Some pits
on the east side of road, three-<]uarters of a mile south of WiUingham, show
4 feet of brown rather fine gravel, with patches of sand and loam.

The Chatteris and March gravels being within the borders of the Fen have
been described by Mr. Skbrtchly, but we may record our opinion, based upon
their direction, level, and character, that they are an extension of these ancient
river deposits, but judging from the shells at the latter place, that they repre-
sent their marine teimination.

In the neighbourhood of Newmarket there are many other
patches of gravel arranged in similar lines, but belonging ap-
parently to a different river system, of which only a small part
comes within our area. These patches commence in the valleys that
drain the hill slopes by Westley Waterless, DuUingham, Ditton,
and Cheveley (in 51 S.E.), and form several series which appear
to converge near Exning, whence a gravel-capped ridge extends
still farther in a northerly direction.

About two miles west of DuUingham there is a spur of chalk running out
from the hills and separating two deep valleys ; at the northern end of this,
and about half a mile S.S.W. of DuUingham Heath Farm, is a smaU patch
of gravel resting against the flank of the hiU ; a pit here showed four feet of
fine gravel and brown sand with angular flints, some standing on end.
Another smaU patch occupies a similar position on the western side of the spur.

North-west of these, by Bungalore Bam, there is a third outUer, and a
much larger spread caps the ndge which stretches thence by Upper Hare
Park across the road from Cambridge to Newmarket ; this has been excavated
in several places for gravel, but no good exposure was seeu.

A thick red graveUy soU covers the ground west of New England Farm, and
marks the former extension of the deposit ; the ridge then trends to the N.E.,
and there are gravel pits on the high ground between Partridge Hall and the
Devil's Ditch ; the westernmost of these gave the following section in 1876 : —

Feet. '
Brown sandy soil - _ - - i

Hard marly clay with stones - - - 3

SmaU gravel with large stones at the bottom - 1
Hard clayey sand passing into brown loam - 4

Excavations in other parts of the pit showed hard stony loam with flints and
other stones impacted in it, and thin layers of chalky or marly matter, the
whole looking like re-arranged Boulder Clay ; but at one place softer laminated
loam with similar marly layers was seen, about four feet being exposed.

The second pit, 2 furlongs N.W. of the above, showed 8 feet of gravel, com-
posed chiefly of small flints and chalk pebbles with a few larger stones ; the
lower part was distinctly bedded, but the top was confused and piped with
brown sandy loom.

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92 GEOLOGY OF THE NEIGHBOURHOOD OF GAMBBIDGE.

Another outlier of similar material occurs on the next elevation to the N.E.,
overlooking the village of Exninff ; a small pit in this showed angular gravel
of irregular thickness overlying dialky loam, 4 feet of the latter heing visible.

East of Exning a second Une of gravels comes in from the S.E., marking
the course of an important stream which must have passed over the site of
Newmarket ; the conunencement of this series lies outside our district in the
neighbourhood of Cheveley, but we observed some thickness of gravel resting
on the flank of the hill about a mile S.E. of Newmarket, and fig. 19 represents
the section then seen in the pits marked on the map.

Fig. 19. — Section in Gravel Pit^ half-mile S.E. of Newmarket
Railway Station,

Feet.

g. Angular gravel in chalky matrix (the upper 3 or 4 feet
brown, and piped into the lower part by diasolution of
the Chalk) showing some lines of stratification - - 12

/. Fine chalky gravel, horizontal - - - - 4

e. Yellow sand on the edges of <^ - - - \

(L False-bedded fine chalky gravel inclined 20° to N.E.

(«.«. towards the valley) - _ - - J

c. Fine chalky gravel. I

b. Yellow sand. I - - - - - 2

a. Fine gravel. J

North-west of Newmarket a long ridge conmiences which is capped with
gravel for a distance of more than a mile.

The large pit W. of the Union House gave, perhaps, the best section of
thsee gravels in our district; it was as follows in 1876 : —

Feet.
White gravel, consisting mainly of chalk pebbles - - 6-8

Sub-angular flint«gravel, with some chaU^ pebbles and small
patches of sand ; greatly contorted and very hard, so compact
indeed that it stands like a wall when cut out in square bays
the whole depth of the pit, about - - - - 25

Sand, very coarse and gritty at the south end and fine at the
north end of the pit - - - - - - 8

The contorted bedding of the gravel is probably due to the dissolving away
of the Chalk beneath.

Gravel pits by the road side half mile N.W. of the Union House showed
6 feet of hard angular flint gravel.

From Exning the ridge turns to the N.E., and the pit one mile N.E. of the
church exhibited the following beds ; —

Feet.
Brown sandy soil with flints - - - - 2

Hard chalky sand with flints - - - - 4

Loose chalky gravel and sand - - - - 3 ?

Sharp bufP-coloured sand - - - - - 2

Between these two series there are some other patches of gravel
which may indicate a tributary stream ; they occur on Ling Hill 2i
miles S.W. of Newmarket, and along the ridge which runs south-
ward by Shuckburgh Castle.

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POST-GLACIAL DRIFT. . 93

The railway cutting west of Dullingham Station exposes a very good section.
It shows Chalky Boidder Clay, with some large boulders, resting on the Chalk,
and probably at this point occupying a slight hollow therein, as it usually
does where the *' hard bed " occurs,— here that bed forms a prominent line along
the sides of the cuttings. At the west end there is angular gravel with yellow
sand resting directly on the Chalk, it has been dug for ballast from a large
pit on the north side of the railway. Thus within a short distance are two
deposits each resting directly on the Chalk, and it is difficult to determine
which of the two is really the uppermost, as the old ballast pit, from slips and
overgrowth, is all in confusion.

The gravel is on the same level, and appears to be of the same character as
the Post-glacial patches to the west, but on the south side of the cutting (oppo-
site the ballast pit) it is overlaid by what looks very miioh like Boulder Clay.
The day, however, which is stratified and of slight thickness only, may perhaps
be regarded as a wash from Boulder Clay at a higher level, or the gravel seen
beneath it at that particular point may be the first setting in of the beds
which occur beneath the Boulder Cla^ in the direction of Bury St. Edmunds.

Just west of Dullingham cutting is a patch of angular flint gravel, with
brown and buff sand, small in extent and thickness.

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94 GEOLOGY OF THE NEIGHBOUEHOOD OP OAMBEIDQE.

CHAPTER IX.-POST.GLACIAL DRIFT— (continned).
Gravels of the present River System.

These gravels cover a considerable extent of ground in the
neighbourhood of Cambridge. There are small patches along the
courses of all the main streams at two or three levels, now on one
side, now on the other ; and where these streams converge near
Grantchester the gravels begin to occupy more ground, and in a
fairly wide spread continue all the way to the fens.

The time which elapsed between the deposition of the gravels,
of which an account has just been given, and those we have now
to describe must have been very great. There was time in the
interval for an entire change to take place in the drainage system
of the country, the old channels were deserted, and the rivers were
finally directed into the valleys in which they now flow.

Cam System. — Highest Terrace.

The highest terrace of gravel connected with the present river
system has been called the Barnwell series, because of the good
sections in it at that place, where it also attains its greatest
thickness.

We have seen that in early Post-glacial times a stream issuing from Ward'
ington Bottom flowed to the N.E, towards Triplow and Whittlesford to join
the river which then occupied the main valley of the Cam. It appears,
however, that this stream gradually changed its course, swinging to the north-
ward, and eventually turning north-westward from Foulmire to Foxton, so
that its waters were deflected into the tributary valley of the Rhee. It is
probable that at this early period the country lying to the westward was still
covered with Chalk and Boulder Clay, and that the present channel of the
Rhee above Barrington had no existence, for it is entirely supplied by springs
from the Chalk Marl, which could not then have been in their present
positions. {See post, p, 125,)

The deflection of what we may call the Wardington river was doubtless
gradual, and it is difficult to determine the exact age of the gravels which
occur at intervals and mark out its newer course. Their patchy mode of
occurrence is evidence that they are very old and that the subsequent denu-
dation has been very great ; again it is probable that a greater quantity of the
gravel was brought down from the Chalk escarpment, and was deposited in early
times, for the power of the stream has now so declined that it can no longer
carry down sucn heavy detritus, and there are no recent beds of gravel along
its course. It seems likely therefore that the patches of gravel near Foulmire,
Foxton, and Harston are the earliest beds belonging to that valley, though we
cannot be quite certain of their contemporaneity with the Barnwell gravels.

Near Barrington, on the opposite side of the Khee Valley, there are two small
patches of gravelly silt, which have recently acquired much importance from
the remarkable number of manmaalian remains obtained from them. These
deposits have been described by the Rkv. O. Fisher, to whose paper we refer
for particulars.* "We agree with him in thinking that they belong to the same
terrace as the gravel near Foxton, but we fail to see in them any proof that the
valley of the Rhee west of Barrington had anything like its present extension.

We consider that the main stream at this period came from the south-east
as above stated ; since, however, its further course in a northerly direction
would be barred by the Orwell and Barrington Hills, it was forced to turn to

* Quart, Journ, Geol, Soc, vol. xxxv., p. 670.

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POST-GLAOIAL DRIFT. 95

the N.E.^ fin(Hng an outlet where the action of springs had caused a f^ap in
the ridge. Such a deflection and obstruction would very probably result in
the fonaation of a large " broad," or lake-like expansion of the river, between
Foxton and Barrington. This hypothesis will, it appears to us, account for all
the phenomena described by Mr. Fisher, and will explain the great difference
between the . Barrington and Foxton deposits, for all the coarse gravelly
material brought down from the southern hills would be deposited at the
debouchure of the stream into the southern end of this lake ; while in the
quiet waters along its northern shore a very different set of beds would be
formed, consisting only of the materials derived from the local denudation
of the chalk slopes on the west and the clay-capped hills on the north ; the
product would be a strong silt or marl, and the circumstances would be
favourable for the accumulation and preservation of organic remains. The
action of springs may have given a westerly extension to this lake.
The sheUs found at Barrington are the following :—

Helix caperata (conunon). Succinea oblonga?

„ nemoralis (rare). LimnaBa palustris.

„ virgata (common). Pisidium amnicum.

The Mammalian remains are listed on p. 106.

In the valley of the tributary which comes from the S.E. by Linton and
Abington there are similar patches of gravel at a corresponding height above
the present stream. Some pits north of Pampisford Station showed 10 feet
of whitish stratified gravel at the north end of the pit, somewhat contorted,
and enclosing patches of loam with shells {Limnea, Pupa), Loam is exposed
at the angle of the pit, and seems to be banked up against the gravel.

On the hill about a mile N.N. W. of Sawston there is a gravel pit in a small
outlier which may once have been connected with the series of gravels we
have now to describe.

The first patch of gravel, which can be identified with certainty as forming
part of the Barnwell series, occurs just beyond the confluence of the two
streams, and caps the high ground to the N.W. of Shelford. The southern-
most end of the old channel is cut through by the railway from Cambridge
to Hitchin ; the middle of the cutting is in Chalk Marl, but at the western
end, just before the river bank is reached, the following section is seen : —

Feet.
Gravelly soil - - - - - - 2

White sandy marl, very hard - - - - 1

Soft white sand with shells - - - - 1

Fine yellowish gravel - - - - - 2

The whole passes eastward into white calcareous sand, and rests against
the chalk slope. The following species of MoUusca were found :

Bithinia tentaculata. Valvata piscinalis.

Helix arbustorum.

„ ericetorum. Cyrena fluminalis.

„ sp. Pisidium, sp.
Flanorbis, sp.

On the hill northward are some old gravel pits marked on the Ordnance
map, but now ploughed over. The gravel-capped ridge which here marks
the ancient course of the river forms a strong contrast to the low plain of
more recent gravel westward. A second old gravel pit occurs near Vicarage
Farm, and further north gravel was seen at several places in the cutting on
the Bedford and Cambridge Railway. Between the bridges half a mile south
of Trumpington, gravel and sand was seen in the bank, with a bed of hard
yellowish-white sandy loam at the base, resting immediately upon clunch.
By the 28th milestone (eastward) clunch rises again from under gravel and
possibly separates two terraces.

The well at the Green Man, Trumpington, is said to be 23 feet through
gravel and sand to clunch. At a coprolite pit half a mile N.N.E. of the
church gravel occurred in irregular pockets and trenches 3 or 4 feet deep,
being let down into hollows by the solution of the underlying clunch, the
intervening tongues of which arched over and sometimes nearly met above the

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96 GEOLOOT OF THE NEIGHBOURHOOD OF CAMBRIDGE.

f(ravel-filled hollow. In one of these part of a tooth of Elephas primigenius
was found.

A small jj^avel pit near Clay Farm on the south-east side shows a few feet
of rather coarse gravel and sand.

The river in which the Trumpington gravels were deposited had not there-
fore cut down to the Gault, but banked its gravels against a chalk slope
which was probably continued over the valley in which the Cam now flows ;
Chalk Marl crops out between the two series of gravels, but the slope of its
surface is now westward in an opposite direction to what it must have been
when the Trumpington gravels were formed, for at that time it must have
sloped eastward. The diagrammatic section (Fig. 20) illustrates this, and
indicates the great amount of detrition which has taken place in the interval
since the period of the older gravels.

lig. 20. — Section across the Trumpington Gravels.

Nine Welk
Railway. Railway.

Horizontal scale, 2 miles to an inch. Vertical scale, 200 feet to an inch.
X X » 8ea-level. The broken line = the form of the surface when the gravels
d were deposited.

a. Alluvium ; 6, c, d = Gravels of the three terraces ; e, Chalk ; /, Gault.

Near Trumpington the main stream seems to havs been joined by a tributary
coming from the west, which has left its traces in a series of gravels extending
from Comberton by Barton and Grantchester.

The patch of gravel upon which the village of Comberton stands rests partly
on Boulder Clay and partly on Gault, and its materials were probably
brought down by brooks draining off the high Boulder Clay land, like those
feeding the present Bourn Brook. Prof. See ley has recorded the occurrence of
Rhinoceros tichorinus in the Comberton gravel. Two small patches of gravel
lie to the south-east of this, and serve to show the former continuity of the
Comberton and Barton gravels, a small brook which drains off Comberton
Field having here made a breach in the old gravel ridge. From a point about
three-quarters of a mile west of Barton Church this ridge may be traced con-
tinuously through Barton and across the fields to Grantchester, the gravel
resting now on Gault, now on Chalk Marl, according to the inequalities in the
sur&ce of the latter; its relations to the present surface are shown in Fig. 20,
which crosses the ridge about a quarter of a mile W. of Grantchester Church.

There are small gravel pits near the road about the same distance N.W. of
the church, and the gravel ihas been more extensively dug in the paddock
between the vicarage and the church ; fine flint gravel interbedded with sand
was shown here to a depth of about 8 feet in 1875, and we were told that
large bones had been occasionally found in it. The ridge of gravel ends
abruptly bdow the churchyard wall, but was doubtless continued originally
across the present valley of the Cam to join the Trumpington ridge near Gay
Farm.

From Trumpington the river-course appears to have turned north-eastward
below Clay Farm, but it is here cut '.through and breached by the newer series
marked c in the above diagram. It is found again, however, on the opposite
slope by Brooklands Farm and Hinton Cottage. Large gravel pits have been
opened between the latter and the railway, and these were from 7 to 10 feet
deep in 1876. The soil consists of a dark brown gravelly loam, which is
removed over some square yards, leaving an undulating surmce of the harder
gravel below; the latter consists mainly of flint and chalk pebbles, with a bed
of white silty marl near the bottom, underneath which is a layer of coarse
gravel resting upon the chalk. The workmen stated that they had found
bones and shells in the white marl.

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POST-GLACIAL DRIFT. 97

At the railway siding below Brooklands Farm, a similar sectioa was shown,
as follows : —

Feet.
Gravelly soil - - - - - 2

Fine bedded gravel and sand, quite unoompacted

and in places stained nearly black - - - 6

Clunch touched below.

In 1876 the bank opposite the Cambridge Railway Station was cut back
for widening the line, and a section of the gravels was thus exposed.

Near the goods sheds this was 16 feet deep, showing first loamy soil, then
fine gravel and sand, with thin interbedded layers of greyish white loam and
coarser gravel below. These beds thinned out to 8 or 10 feet of sandy gravel
near the junction with the Newmarket line, and were seen to rest upon an
uneven surface of Chalk Marl, in which many flint pebbles were impacted.
Chalk is cut through further along the Newmarket line, but has occasional
pockets of loamy gravel.

The excavations made for the foundation of the houses along the road west-
ward from the station were 10 or 12 feet deep in gravel ; in those nearer the
Hills Road the thickness of gravel was less, and Chalk Marl was found below ;
the surface of this gradually rose till nothing more than a thin gravelly soil
lay above it, and the foundations of the houses at the junction of the roads are
in chalk. It is clear, therefore, that between this point and Polecat Farm the
gravels still lie in a channel cut in the Chalk Marl as they do near Trumping-
ton.

A quarter of a mile north of the railway station there is a small pit near the
chapel in Mill Road from ^ to 10 feet deep in fine gravel and sand, with thin
lenticular beds of white marl resting on a dry white clay, which undoubtedly
belongs to the lower part of the Chalk Marl; the surface of this sloped east-
wards. Some bones in bad preservation, but apparently belonging to an ox
{?Bosprimigenius)f were found in one of the sandy layers. Portions of the gravel
were compacted into a dark brown iron stained conglomerate.

In foundations for houses east of the cemetery 7 or 8 feet of sandy gravel
was observed resting on similar white clay. The same gravel, with loamy or
marly layers, underlies the cemetery itself, and extends westward to the comer
of Parker's Piece, overlapping on to the Gault, and thinning out, so that the
latter comes to the surface. Along the East Road there is generally a good
depth of gravel, Gault being reached at varying depths of 10 to 20 feet.

Fuller's gravel pit, about a quarter of a mile N.E. of the Cemetery Chapel,
exhibits a good vertical cutting into these gravels ; the exposed face is about
10 feet deep, but the workmen stated that the gravel extended to a depth of 14
feet, and that it was underlaid by Chalk Marl, with the coproUte bed about 20
feet from the surface. The upper part of the gravel is much contorted, and
long narrow pockets or pipes descend almost vertically downwards, these being
filled with dark brown sand and stony loam form a marked contrast to the
yellowish-white chalky gravel into which they penetrate. In some of them the
bottom is lined with a stiff, brown, stony clay, and the roots of the trees and
bushes, which doubtless gave rise to these pockets, are still to be seen.

Northward of this pit gravel is to be seen in several excavations, and the
coprolite bed has been worked out under it for some distance.

Much gravel is now obtained from a pit on the southern side of the
Barnwell main road nearly opposite the Aboey Church ; this exhibited a suc-
cession of light coloured sands and fine gravel (often obliquely bedded) with
bands of loam and marl similar to that which has been so often noted in the
Abbey pits. In 1874 the section here was as follows : —

Feet.
I»amy soil with roots penetrating into the bed below - 1 to 1 J
Dark sand and gravel, contorted and filling hollows in 1
the marl - - - - - ->4to5

Whitish chalky clay or marl - - - - J

Yellow false-bedded sand - - - - 3 or 4

Sand and gravel, evenly bedded, with thin layers of marl 7 or 8
Clunch, touched at one corner.
The thickness of the several beds changes as the section is cut backwards,
but the top few feet is always more or less contorted, and the coarser gravel lies
N309. a

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98 GEOLOGr OP THE NEIGHBOURHOOD OF CAMBRIDGE.

aear the bottom resting on Chalk Marl, which underlies the pit at a depth of
6 or 16 feet. A tooth of Rhinoceros tickorhinus was obtained here together
with bones and teeth of Equus fossilis; and in 1878 Mr. A. F. Griffith
obtained a fine flint-hache* from this locality.

In fonner years the excavations for gravel on the site of Barnwell Abbey
afforded excellent sections which have been described by several observers,
especially the Rev. P. B. Brodie in 1844t and Prof. Seeley m 1866.J A
flint-flake was found here in 1862 by Mr. Whitaker.§

The general succession as deduced from the descriptions given at different
times seems to have been as follows : —

Feet.
6. Soil and disturbed gravel - - 3 or 4

5. False-bedded sands - - ]

4. Layer of white marly loam - - >■ 10 to 14

3. False-bedded sand and fine gravel - J
2. Brown marly clay or loam - - i to 4

1. Coarse pebbly gravel - - 2 to 4

Total - - - 20 feet.

Nos. 3 and 4 were the most fossiliferous layers.

ITie upper part of the section was still visible in 1875, and was as follows :—

Feet.
Gravelly soil - - - - - 2

Sand and gravel, disturbed in places - - 2

Laminated greyish-white loam, becoming sandy

and yellowish below - - - - 4

Fine gravel with layers of sand - - 6

Gault was found below the gravel in this part of the pit, but behind the old
Abbey wall the bottom was found of clunch, and the gravel was not more than
7 or 8 feet deep, thickening towards the main road, A section through these
pits would therefore be as in Fig, 21.

JFig. 21. — Section across the Barnwell Gravels.

N.W.
River. Priory. Road. Pit. S.E.

Horizontal scale, 50 yards to an inch,

X X Sea Level. a Alluvium. b Gravels. c Chalk Marl, d Gault

The gravels are chiefly composed of flint pebbles, but pebbles of chalk are
frequent and phosphate nodules from the base of the Chalk Marl are not
uncommon. Larger blocks and boulders were also found occasionally, heaps
of which, as they had been thrown aside, were still to be seen in 1875; these
consisted of various kinds of rocks, such as granite, gneiss, quartzite, basalt,
and porphyritic felstone, with limestone and other sedimentary rocks. All
these fragments have doubtless been derived from the Boulder Clay, but they
are no proof that any Boulder Clay was then in close neighbourhood to the
river ; most of them were probably derived immediately from the destruction
of the older river gravels through which the Barnwell stream must here have
cut its way, and before they found their way into these beds they naay have
formed part of still older gravels like those capping the Gog-Magog Hills.

* Geol Mag,, Dec. EL., vol. v. p. 400..

f Cambridge Phil. Trans., vol. viii. pt. 1. p. 138.

X Quart, Joum. Geol. Sac., vol. xxii. p. 475.

§ Evans' Ancient Stone Implements, p. 485, London, 1872.

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POST-GLACIAL DRIFT. 99

The Barnwell gravels were in their turn cut through by the river when it
flowed through Chesterton, and formed the gravels which stream away to the
northward by Milton and Waterbeach ; but when the beds of gravel, sand, and
marl were being deposited under the site of the Abbey grounds the eastern
bank of the river curved round in all probability across the present course of
the Cam, and was continuous with the island of Chalk and Gault on which
the windmill N.W. of Chesterton stands.

Between this island and the similar outlier north of the Castle Hill is a
trough nearly half a mile wide and filled with gravel and loam, in which there
were once many pits, but none are now open. Some years ago, however, there
were gravel pits near the eastern end of Victoria Road, and their section was
observed by the Rev. O. Fisher, from whose paper the following is taken : — *

Warp.

White sandy brickearth.

Yellowish sandy earth.

Fine sandy gravel.

Yellowish brickearth.

Fine gravel, more contorted than the layers above and below.

Sand.

It will be seen that these beds form a succession very similar to that in
the Barnwell pits ; the sands contained Bithinia and other small shells, but no
specimens of Cyrena fluminalis were found. Mr. Fisher comments upon the
curiously eroded line of junction between the "warp" and the subsoil in this
and other instances. He considers it to be the intersection of subterranean
channels of drainage, along which he believes there is a slight forward move-
ment of the particles of the soil or warp. **This," he says, "may account for
the flat-topped elevations, like the tenons in the framework of a dissected
puzzle, which often occurs near the line of junction of the warp with the sub-
soil, especially (if I mistake not) where the latter contains calcareous matter
and has suffered partial solution. The erosion at the bottom of two contiguous
subterranean channels would leave an elevated ridge between them, and the
superincumbent soil sinking in a general mass would then flatten the crest' of
the ridge." We quite agree with this explanation, and have observed siniilar
instances in many of the coprolite pits near Cambridge, where the clunch is
covered with a gravelly soil, particularly at Trumpington, (see ante, p. 95)
where Professor See ley also noticed "the great extent to which the upper
2 or 3 feet (of the gravel) are contorted and folded.*

Northward from the trough or channel above mentioned the gravels spread
out over a larger area towards Impington and Histon. In the ditch which
runs through the fields toward the old camp at Arbury fine yellow gravel is
seen at the southern end, and reddish-brown laminated loam where it passes
under the road east of Arbury ; and its continuation eastward is dug through a
considerable thickness of gravel and sand, compacted in places by a ferruginous
cement as to form a hard conglomerate, lumps of which are scattered over the
fields. Where the ditch runs by the new roadway about a mile east of Arbury
a black peaty loam was exposed in the bottom of the ditch underlying about
5 feet of gravel and sand.

At the farm on the road west of Arbury the well was dug through 9 feet of
gravel into a quicksand with water, and a similar supply of water was obtained
at the windmill south of Histon Station.

The same gravel and sand, occasionally compacted by ferruginous matter,
is to be seen along the ditch or watercourse which runs through the fields
north of Hogs Hall, and passing under the railway traverses the village of
Histon, then turns to the N.W. and cuts through the older gravels between
Histon and Oakington ; this brook has, of course, re-arranged portions of both
series.

That which we have called, for convenience sake, the Barnwell series has
suffered much denudation in the neighbourhood of Histon and Impington,
and it is impossible to unravel the history of all the patches of gravel, sand.

* Quart, Journ, Geol. Soc., vol. xxii. p. 551.
f Quart » Jounu Geol. Soc, vol. xxii. p. 475.

G 2

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100 GEOLOGY OF THE NEIGHBOUEHOOD OF CAMBRIDGE.

and loam which occur in this district. The gravel capping the rising ground
in Impington Park may belong to some older formation, but it seems to be
connected with the loamy deposit on which the church is built, and this
appears to run down to lower levels ; north of the church are some excavations
in a soft yellow sandy loam, very clean and somewhat laminated, which is seen
again in the brickjrard to the eastward, where it is rather more stony. In
another part of this brickyard pockets of loamy gravel containing lar^e
boulders descend into the Gault, the stones and rocks being such as would
have been washed out of neighbouring Boulder Clay ; similar yellow loam is
to be seen in ditches about half a mile south-eastward.

East of Impington these gravels have been aknost entirely swept oS the
surface of the country, the only traces of their previous extension being
found in two long and narrow channels filled with sand and gravel, which
are prolongations from the main mass near Kings Hedges ; they are intersected
by tne numerous ditches which here separate the fields, and by means of the
evidence thus afforded the gravel-filled channels were traced over the ground.
Their terminations point across a shallow valley north of Impington (formed
by a more recent line of drainage) towards an outlying gravel-covered plaia
which stretches north and north-east of Histon.

At the fork of the roads, nearly half a mile N.E. of Histon Church, there
is a thickness of from 6 to 10 feet of gravel above the Gault, and further
in the same direction gravel has been extracted from several places in the
fields ; it is everywhere composed of small pebbles of flint and chalk, and
much sand appears to be mixed with it. This gravel plateau is cut off quite
suddenly along a line running nearly due east and west, so that there is a
straight terrace-like descent, nearly a mile long, on to the lower plain formed
by the Gault towards Cottenham.

No patches of gravel have been found north of this line, and it does not
seem probable that the series we have been tracing was ever continued across
the ridge of high ground (formed by the outcrop of the Lower Green sand and
Kimeridge Clay) which runs north-eastward from Oakington to Cottenham.
This ridge, at the time we are treating of, was doubtless even higher than it is
now, and we know that from Oakington southwards there was also high
ground capped by the more ancient river gravels.

Thus the outspread of gravel about Arbury, Impington, and Histon seems
to have been accumulated in a kind of lake or wide reach of the river,
in which there may have been Gault islands, separated by the deeper channels
made by the stream as it changed its course from time to time. From this
lake or " broad " there could be no outlet except in one direction, N.E. by
Landbeach ; we are therefore led to inquire whether there are any indications
of the former continuation of the gravels in that direction.

Now N.W. of Milton there occurs a long outlying patch of gravel, separated
from the newer series by a Gault slope, and traversed along its whole length
by the old Roman road ; gravel to a depth of at least 4 or 5 feet is shown in
the ditches on either side of this road, and the elongated extension of the
outlier points northward to another small patch in the fields a little more than
half a mile N.W. of Landbeach Church.

These indications, therefore, seem to confirm the surmise that the Barnwell
gravels were once continued in a north-easterly direction from Histon ; but a
newer series, that, namely, which extends from Chesterton through Milton,
here intervenes, and again cuts through what appears to have been the course
of the older gravels, consequently all traces of their occurrence in this district
are destroyed or obscured. It is interesting, however, to find that by the form
called Denny Abbey certain patches of gravel seem to separate themselves from
the newer deposits, keeping at a somewhat higher level, and it is quite possible
(not to say probable) that these belong to the older Barnwell series ; we have,
therefore, ventured to indicate this on the map (PL 4) as the course of the
river during this period.

Denny Abbey stands on the first of these patches, which forms a gravel-
capped ridge, elongated towards the N.E., and nearly surrounded by slopes of
Gault, except on the western side, where newer loams have been banked up
against it. By Causeway End Farm gravel again occurs, and the house called
High Elm, still further N.E., stands on another small outlier which forms a
kind of island surrounded on three sides by the fen.

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POST-GLACIAL DRIFT. 101

Beyond this point the continuation of the series has either been entirely
swept away> or is to be sought for below the fen deposits towards Streatham
and £ly.

Gam System. — Intermediate Terrace.

In the tributary valleys of the Cam many patches of gravel
appear to occupy intermediate levels between those beds we have
described and the more recent deposits bordering the course of the
present streams ; such are found near Abington and Babraham,
and in the main valley near Chesterford, Duxford, and Whittles-
ford. It is impossible, however, to separate these from the gravels
of earlier or later date^ for the river, in shifting its channel, has
continually removed and re-arranged previously deposited beds, so
that in many places a continuous slope of gravel has been formed
without any separation being visible between the diflFerent stages
or terraces.

With regard to the age of the gravels in the valley of the Rhee,
we have already pointed out that the materials were brought down
by the stream issuing from Wardington Bottom, and have mdicated
the difficulty of correlating the deposits with those in the main
valley near Cambridge.

Similar difficulties stand in the way of discussing the relative
ages of the gravels in the valley of the Bourn ; some of the patches
are at a higher level than the others, but probably no two are
exactly at the same relative level or of precisely the same age.

It happens, however, that between Shelford and Cambridge a
continuous deposit of gravel has been preserved, occupying an old
channel, which was evidently the course of the river at a period
later than that of the Barnwell gravels and before the time when
the present channel below Shelford was formed.

If the general direction of the Cam valley be prolonged from
Whittlesford through Great Shelford, the line would pass along the
low ground which stretches northwards between the Chalk Hills
on the one hand and the low ridge formed by the Trumpington
gravels on the other ; it is this strip of low ground which is occu-
pied by the gravels in question (see Fig. 20, p. 96).

Shelford and Stapleford stand at the entrance to this channel, and gravel is
or has been shown in many excavations about these villages, but so many
different river courses seem to have converged towards this locality that a
complete disentanglement of the several gravel terraces is well-nigh impossible.
The following exposures were noted in 1876.

In a saw pit about a quarter of a mile S. of Stapleford Church 6 feet of
gravel and interbedded chalky sand were seen ; the well in cottage garden
near by was stated by the well-sinker to be through 8 feet of sand into white
clay or clunch (12 feet).

A pit in the field between the river and the main road near the old turnpike
showed about 8 feet of coarse gravel, indistinctly bedded, with occasional
patches of fine sand.

At Great Shelford there is said to be from 8 to 10 feet of gravel in the
churchyard ; the gravel pit about 100 yards N.W. of the church exposed 6 or
7 feet of gravel and sand.

The railway cutting south of the station showed pockets of sandy gravel
and loam overlying the clunch, passing into a bed of gravel 8 feet deep, which
was at one time worked in the yard of the Station Inn.

From a field opposite the Greyhound Inn, half a mile N. of the church,
much gravel has been obtained, and also from the railway cutting close by.

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102 GEOLOGY OF THE NEIGHBOUBHOOD OF OAMBEIDGE.

where 8 feet of sandy gravel is seen overlying white clay (? Chalk Marl) ;
Succinea, Helix sp,, and Ackatina acicula were found here.

The average depth of the gravel at the northern end of Shelford is 10 feet.
Along the ditch or watercourse running thence N.N. W. gravel is seen in many
places, overlaid in some of the side-ditches by a whitish clay containing shells ;
Helix hortensis, H. rufescens ?, Bithinia tentaculata, Succinea putrisy Planorbis
marginatus, and Pisidium amnicum were collected from this clay, which is
doubtless much more recent than the underlying gravel.

The water issuing from the " Nine WeUs '* near ** Steeple Hill " runs west-
ward to join this watercourse, and the stream below their union is known as
" Vicars Brook." The gravel continues to border both sides of this, with an
average breadth of half a mile, and opens out into the great spread of gravel
upon which most of Cambridge is built. A pit close to the brook, a quarter
of a mile S. of the point where it crosses the Trumpington Road, showed the
following section : —

Fine flint gravel and sand, with strong springs issuing from the base, 6 feet.

Bluish-grey clunch, with dark glauconitic marl at the bottom, 9 feet.

The plot of ground called Coe Fen, opposite the Botanical Gardens, has been
worked^ over for gravel, and the gardens themselves stand upon 7 or 8 feet of
the same material, the bottom of the pond being in the Gault ; the Chalk Marl
and coprolite bed probably crop out under the gravel near the hothouses, for
a well outside the N.E. corner of the gardens pierced about 8 feet of soil and
gravel, with 6 feet of clunch below, and another at the eastern end of Norwich
Street was dug through gravel (6 feet), " white clay '' (7 feet), *' coprolites "
and Gault (1 foot).

At the house called the Leys excavations for new buildings showed only
1 feet of gravel and sand over Gault. A deep trench, opened for drain work,
along Trumpington Road from the corner of Downing Terrace exhibited this
section at the N. end : —

Bedded gravel and sand, 8 feet.
Loose quicksand, with water, 2 feet.
Gault clay, 6 feet.

The surface of the clay, however, rose rapidly southwards, little or no gravel
being found above it at a distance of 20 yards in that direction.

A similar trench leading from the pavilion in Fenner's Ground to the Hills
Road gave the interesting section shown in Fig. 22, the gravel here being
backed up against the Gault.

Mff. 22. — Section along Drain from Fenner^s Ground to Hills Road,

S.W. Cambridge, N.E.

Hills Eoad. Hedge. Pavilion.

+ Bottom of drain. (•) Level of Cam.

a. Gravel. 6. Chalk Marl. c. Gault.

This ridge of Gault extends northwards across Parker's Piece, by the
eastern side of Christ's Piece and New Square, to Maids Causevray and Butts
Green, thus separating the Barnwell Terrace from the newer gravels under-
lying the rest of Cambridge ; it is not unlikely that the gravel at the northern
end of the town from Corpus College to Midsummer Conunon may be more
recent than that found to the southward by Downing College and the
Botanical Gardens, for the level of the latter district, south of Downing Street,
averages 11 feet higher than that of the former. The following is a list of
places in the town between the river and the ridge of Gault above-mentioned,
where recent excavations have shown a greater or less depth of gravel.

Downing College (new buildings, 1875), 8 feet of gravel and sand over Gault.

Pembroke CoUege (new buildings, 1875), 7 feet of gravel, Gault seen below.

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POST-aLAOIAIi DRIFT, 103

Opposite Police station, about 8 or 10 feet of gravel.

St. Andrew's Street, foundations of house near Mr. Sayles, 8 feet of sandy
gravel over Gault.

New Corn Exchange, 10 feet of gravel above Gault.

Caius College (new buildings), 10 feet of gravel with much water at the
bottom.

St. John's Chapel, 4 feet of gravel with Gault below.

Comer of Jesus Lane, 15 feet of gravel said to have been found in digging
a well, with yellow loam below, resting on Gault.

A well-marked terrace of gravel occurs on the west side of the river, and
extends from Croft Town through Newnham to Trinity College Gardens ; the
level of this terrace is probably much the same as that by New Town and
Downing College, or about 40 feet above Ordnance datum.* The average
depth of the gravel as seen at several places in Croft Town, at Newnham Hall,
and in Parallelogram Road, is about 9 or 10 feet.

At Chesterton similar gravel occurs at about the same level, and has been
extensively worked in the fields bordering the northern side of the river south-
west of the church.

The pits open in 1875, 7S exposed 12 feet of gravel with occasional seams
of fine sand, and water coming in at the bottom prevented deeper excavations.
The gravel is mainly composed of flints, but quartzite pebbles, fragments of
Oolitic limestones, and of various igneous rocks not unfrequently occur.
Many bones have been found in these Chesterton gravels, and some are
preserved in the Woodwardian and Anatomical Museums. The thickness of
the gravel appears to lessen towards the N.W., the following section being
visible (1875) in a small pit near Captain Wragg's house on the Chesterton
road : —

Feet
Dark-brown gravelly soil - - - - 3

Yellowish fine flint gravel - - - - 4

light blue Gault, quite dry, shown below.

Northward from Chesterton this gravel forms a well-marked terrace parallel i
to the river Cam for some distance, and about three-quarters of a mile wide.
Gravel, sand, and loam are shown in many of the deep ditches'^between Ches-
terton and Milton, the stream which had, brought the gravelly detritus thus
far down its channel having apparently sorted and sifted out the coarser and
finer materials into separate beds.

North of Milton this series of beds widens out somewhat, and slightly
changes its direction, passing due north between Landbeach and Waterbeach,
so that a strip of Gault appears between its eastern edge and the alluvium of
the Cam ; a section across the Cam Valley, where this commences about five
furlongs S.S.W. of Waterbeach Church, would appear as in Fig. 23.

Fig, 23. — Section across the Cam Valley south of Waterbeach,
Rail. River. Road.

Vertical scale, 100 feet to an inch. Horizontal, 5 inches to a mile,
a. Alluvium, b. Recent gravel, c. Higher gravel terrace, d. Chalk marl. e. Gault.

A gravel pit half a mile west of the church has been dug to a depth of
7 or 8 feet, and there are several old pits on Landbeach Common whence gravel
has been obtained.

North of this the width of the terrace is about a mile and a quarter, and its
eastern boundary forms a ridge by Windfold Farm, separating fields in which
the character of the soil is entirely different, light sandy ground being found
on the western side, while the soil on the eastern slope toward Waterbeach
Joist Fen is the stiff heavy staple formed by the Gault.

* Roughly speitking, the levels of the three terraces are as follows : — Lowest
terrace, 30 feet ; Middle terrace, 40 feet ; Barnwell terrace, 50 feet.

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104 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

Gravel and sand may be seen in many places along the road to Ely, part of
which is carried along the ancient Roman Way. Gravel pits, half a mile
N.W. of Goose Farm, exhibit about 6 feet of sandy gravel ; the stones are
mostly flints, but rock fragments and phosphate nodules from the Lower
Greensand are plentiful (the outcrop of this formation being just southward),
a few chalk pebbles occur, but these have travelled far and are very small.

This gravel is traceable northward by Long Drove till it passes under ChaflP
Fen, it appears, however, to have suffered great denudation in this district, the
small gravel-pits near the fen showing only 4 or 5 feet of gravelly sand.

One just north of the house at the end of Long Drove showed the fol-
lowing beds : —

Feet.
Black peaty soil (edge of fen) - - IJ

Soft grey silt - - - .1

Fine gravel and sand - - - 3

Fine silt full of water, with Kimeridge
Clay below - - - - U

Another about a quarter of a mile to the S.W. showed : —

Feet.
Black peaty soil - - - - 1

Soft silt and sand - - - - IJ

Fine gravel and sand, interbedded (water at
bottom) ... - 3

Eastward by Denny Abbey it is more loamy, and has better resisted denu-
dation ; hard gravelly loam, with patches of white loamy clay, appears in tbe
bank of the ditch north of the Abbey, crushed shells occur in this, Succinea
and Planorbis being distinguishable. North of this Gaulfc and Lower Green-
sand come to the surface.

Cam System, — Lowest Terrace,

We have already spoken of the gravels forming the lowest level
or terrace at only a slight elevation above the alluvium which
borders the present streams. In the main valley of the Cam an
almost continuous series of such gravel is found below Chesterford
and Duxford, as far as Shelford, but it presents few features worthy
of note. The extensive pits just east of Whittlesford Station
illustrate the position of these beds; the workings are very shallow,
not more than 4 or 5 feet deep, and the gravel is made up of small
pebbles of chalk and flint; there is a bed of greyish loam at the
top, and bones have been occasionally found near the bottom.

Gravels occupying a similar relative position occur in the valley
of the brook commg down from Linton and Bartlow*; at Hilder-
sham, for instance, just north of the Hall, there is 10 feet of
whitish stratified gravel, with patches of sand and loam containing
shells. From Abington to Stapleford the south side of the stream
is bordered by a continuous tract of gravel, parts of which belong
to this lowermost terrace.

We have also pointed out that the present course of the Cam
below Shelford is quite different from that which it pursued in
older times, when the river passed in a northerly direction through
Shelford, and did not join the combined waters of the Rhee and
Bourn till it reached the neighbourhood of Cambridge. The
channel which it has since cut for itself by Little Shelford and
Hauxton is comparatively moderji, and the gravel flats on either
bank are more recent than the gravels of Great Shelford, and form

* For notes of pits at these places, see Memoir on Sheet 47, p. 72.

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POST-GLACIAL DRIFT. 105

a continuation of the series above mentioned as stretching north-
ward from Whittlesford. PI.,

It would appear, indeed, that in consequence of this change m
the channel a considerable lake was formed in the neighbourhood
of Hauxton; before the outlet by Hauxton Mill was deepened
sufficiently to allow of the free outflow of the stream, the barrier of
Chalk Marl through which it here passes would pond back the
waters and produce a lake over the low ground to the eastward, in
which the gravel brought down from above would naturally be
deposited. The outspread of gravel by Hauxton is at any rate
suggestive of this having been the case.

In 1872 some 6 feet of contorted gravel over Chalk were seen in a pit a
quarter of a mile west of the church and in 1875 the coprolite pits near Hauxton
Mill showed the following section, but the beds change and thin out eastward

towards the road : — ^

Feet.

f Coarse gravel with dark brown stains - - 5

I Fine yeSowish sand - - - - 1

River Gravel-^ Fine gravel - - - - - 1

I Evenly-bedded sand and silt - - - 2i

LFine gravel - - - - - i

r^u n A/r 1 / Grey clunch, rather rubbly - - - 8

Chalk Marl -j^ jy^y^ Greensand, with coprolites - - 1

The tongue of land in the angle between the Cam and Rhee above their
junction is also covered with gravel, but no exposures were seen in it.

The Bourn Brook which next joins the river is skirted by a similar series of
gravels, in a continuous strip from Bourn to near Eversden ; another narrow
band commencing at Fox's Bridge, south of Comberton, where several small
pits are open, and continuing by Lord's Bridge, between the railway and the
brook, till the latter falls into the main stream.

The tract of gravel which borders the alluvium on the eastern side of the
Cam opposite Grantchester is at a rather higher level, and probably belongs
to an intermediate terrace formed by the combined streams of the Rhee and
Bourn, when the main stream of the Cam was flowing on the other side of the
Trumpington ridge.

We have already spoken of the gravel underlying the older part of Cam-
bridge as being at a slightly lower level than that to the south against which it
is banked. The terraces are, however, much more distinct on the western side of
the river north of Newnham ; the road along the " Backs " of the colleges by
Clare Piece, Trinity Paddock, and St. John's Garden being on the lower
terrace, and a marked rise being traceable from this to the higher terrace,
through the gardens belonging to King's, Clare, and Trinity Colleges.

A similar rise or bank appears to separate the intermediate terrace north
of Chesterton from the lower gravel flat forming Chesterton Common, and
extending oearly as far as Milton. This gravel has been worked in the field
close to Chesterton Junction, the pits open in 1875 showing 10 feet of fine
yellowish gravel over a black sandy loam or silt, full of water. The workmen
stated that these beds thinned out rapidly to the N.W., the underlying Gault
rising to within 2 feet of the surface about 100 yards off in that direction. A
fine elephant's tusk, now in the Museum of Comparative Anatomy, was
recently found here.

Similar gravel is worked a little distance northward by the side of the Cam-
bridge and Ely line. Beyond this again, and bordering the northern end of
Milton Fen, is a narrow strip of gravel, banked as before against the higher
terrace, and sloping eastward under the peaty alluvium, the thin end of which
is shown in Fig. 23, p. 103.

On the opposite side of the river there is a small patch by Biggin Abbey,
probably at a somewhat higher level, and near Homingsey is a tract of gravel,
apparently indicating the former incoming of a small tributary from the south.
Gravel has been worked at several places under a thin alluvial covering by
the side of the railway beyond Waterbeach, and it probably underlies most of
Waterbeach Joist Fen, which spreads out between Denny Abbey and Upware.

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106 GEOLOGY OF THE NEIGHBOURHOOD OF GAHBBIDaE.

Gam System. — Fauna of the Gravels.

In the preceding pages an attempt has been made to separate the terraces of
gravel in the Cam Valley, and to give some account of the changes which have
tiaJcen place, and of the deposits which have been successively formed, during
the excavation of this valley and its tributaries.

The following list contains the names of the fossils known to occur in each
of the series described, but it is necessarily only a first attempt. The most
ancient series of river gravels has hardly yet been explored, and the first
column contains only the names of those few species found by ourselves, and
of the animals represented in the collection of bones from the Lark's Hall
gravels, lately presented to the Woodwardian^Museum by Mr. Princb, of
Balsham.

The second column (of the Barnwell Gravel) is more complete ; a good
collection exists in the Woodwardian Museum, and, besides the lists previously
made by Mr. Brodie and Mr. Dewick, we are now able to give some addition^
species on the authority of Mr. Alfred Bell. The Mammalia and Mollusca
lately found at Barrington are also included.

The material for filUng in the succeeding columns is very scanty, large
numbers of bones have been found from time to time in the gravels near
Cambridge, and many are preserved in the Woodwardian and Anatomical
Museums, but a record of the exact localities where they were found has not
always been preserved, so that they are useless for the purpose of the present
list.

List of Fossils from the Gravels of Camcbrxdgeshibe.

0) S

Vektebrata.

Bison priscus, Bojan,
Bos longifrons, Owen.

„ primigenias, Bojan.
Cervus megaceros, Hart.

„ elaphus, Linn.
Elephas antiquus, Falc.

„ |>rimigenius, Blum. -
Equus caballus fossilis, H. V. Meyer
Felis spelaBa, Goldf. - - -

Hippopotamus major, Desm. -
Hyaena spelsea, Goldf.
Meles taxQS, Linn. - - -

Ehinoceros tichorhinus, Cuvier
Sus scrofa, Linn.
Ursus spelseus, Blumb.

Anser

Invertebrata (Mollusca).
Gasteropoda.

Achatina acicola, Miill.
Ancylus fluviatilis, Mull,

„ lacustris, Linn.
Bithinia tentaculata, Linn.
Bulimus Lackhamensis, Mont.

„ (Azeca) tridens, Puli.

„ (Zua) lubrica, Miill.
Carychiunt miuimuin, Miill. -
Clausilia biplicata, Mont.

„ rugosa, Drap.
Cyclostoma elegans, Miill, -
Helix arbustorum, Liniu

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POST-GLAOIAL DEIFT,

107

List of Fossils, &c»—^ontimied.

Warp and
Alluvium.

INVERTEBRA.TA (Mollusca) — Gasteropoda

— cont.

Helix caperata, Mont.

„ concinna, Jeff.

„ ericetorum, Milll.

„ fruticum, Milll.

„ hispida, Linn. - - -

„ lapicida, Linn.

...

• ••

„ nemoralis, Linn.

...

„ pulchella, 3fif//.

...

„ pygmaea, J>/-a;>.

„ rotundata, Milll.

...

„ rufescens, Penn.

- '

X ?

„ virgata. Da Costa

Hydrobia marginata, Mich. -

liimnsea auricularia, Linn, -

„ palustris, MillL

...

„ peregra, Milll.

„ truncatula. Mull.

Paludina contecta, Millet

Planorbis carinatus, Milll.

„ complanatus, Linn,

X ?

...

„ corneus, Linn. .

glaber, Jeff,

„ mtldvLS, Milll.

„ spirorbis, Miill,

„ vortex, Linn,

...

Pupa marginata, Drap,

"x?

,..

"x ?

„ umbilicata, Drap,

Succinea elegans, Risso

„ putris, var. major -

„ „ „ minor -

„ oblonga? Drap, -

Valvata cristata, Milll.

„ piscinalis, Milll, - r

„ „ var. antiqua, Morr.

Vertigo antivertigo. Drop, -

„ moulinsiana, Dupuy

„ pygmaja, Z)ra;>.

Zonites cellarius, Milll,

„ „ fulvus, Milll.

„ nitidus, Milll,

„ nitidulus, jDrajo.

„ radiatulus, -^/rfer

L aniellibranchiata.

Sphaerium (Cyclas) lacustre, Mull. -

„ cornea, Linn,

...

Cyrena fluminalis, Milll,

Pisidium amnicum, Miill.

X* ?

„ f ontinale Drap.

, nitidum, Jenyns

...

„ pulchellum, Jenyns

...

Uuio limosus _ _ -

„ littoralis, Lam.

„ pictorum, Linn.

„ tumidus, Retz, _ - -

...

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108 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

Gravels connected with the Wilhrakam River and Fvlhourn Waters.

In the times of the ancient river-system which has left such
interesting memorials of its existence in the long ridges of gravel
described in a previous chapter, the springs which now rise near
Wilbraham, Fulbourn, and Teversham were doubtless nearer
together and poured their waters into the river which then flowed
westward from Quy-cum-Stow. As, however, the declivities
bounding that ancient valley (see fig. 18) were gradually cut
backward by the action of rain and of the springs themselves,
the sources of the latter would travel backward also and become
more separated from one another.

Eventually after the old channels had ceased to carry off the
main drainage of the country, there would come a time when the
streams from the springs would be directed into the central
ground now occupied by Wilbraham Fen, and being ponded back
by the line of the old river-course would form a lake or marsh
whose level would be determined by the height at which the
waters could escape over the lip of the basin by Quy-water Bridges.
The stream issuing from this would then flow northward to join
the Cam.

There are four principal sources which contributed their supply
to the formation of this lake ; the first rises just to the eastward
of Great Wilbraham Church, and the stream flowing west from
this is called the Wilbraham Water, the second is that called
Shardelows Well, east of Fulbourn ; the springs which rise along
the southern edge of Fulbourn Common and run into Caudle Ditch
form the third source, and the springs supplying Teversham Ditch
the fourth.

Traces of f^ravels still remain which must have been deposited when these
streams ran at a higher level and possibly before the above-mentioned lake
was formed ; thus a patch of gravelly soil occurs at Little Wilbraham con-
siderably below the level of the more ancient series and above the sandy and
gravelly soil which appears to mark out roughly the site of the subsequently
formed lake. Another patch of similar material, and occupying a similar
position, is found to the north of Fulbourn, and is shown in the railway cutting
at its southern edge, where a few feet of loamy gravel are to be seen, pipes and
strings of which descend into the rubbly Chalk Marl below.

Further north the rising ground between Candle Ditch and Teversham Fen
is capped with loamy soil, and prolonging the direction of these two patches
we come to another outlier commencing in the fields six furlongs N.W. of
Quy Mill. The ditches north of this point cut into beds of loam, sand, and
chalky gravel, and the length of the patch is about three-ouarters of a mile.
North of this the fields still present a gravelly soil, and tne series was pro-
bably once continuous with the gravel previously mentioned as occurring to
the N.E. of Horningsey, and extending to the border of the present alluvium
of the Cam.

ITie thin covering of gravel and sand which spreads over the low grounds
east of Fulbourn and passes under Wilbraham Fen was probably deposited at a
somewhat later date than the series above described, and appears to have
formed the floor of the lake which once covered this area. Snallow pits have
been dug at several points in this deposit, near Hawk Mill, for instance, and
also by the cottage on the droveway half a mile N.W. of Frog End. The well
here was said to have been dug through the following beds : —

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POST-GLACIAL DRIFT, 109

Feet.
Black soil ------ 2

Fine f^vel - -* - - - - 2

Yellow sandy loam - - - - 6

Clunch - - - - - - - 1

Finally, as the outlet by. Quy- water Bridges was deepened by
the outflow of the water, the leveil of the shallow lake would
become less and less till it was converted into a mere marsh or fen ;
and it was probably in this condition at the time when the Fleam
Dyke was constructed. The people who threw up this defence
carried it from Balsham to Shardelows Well, where the marsh
began, thence to Quy Bridge there was probably an impenetrable
morass which formed a natural defence, and the line by which the
Dyke is continued on the Ordnance map has no real existence on
the ground ; it was only necessary to defend the country from Quy
Bridge to the Cam at Fen Ditton, and High Ditch Lane is the
true continuation of the Fleam Dyke.

The Fen has been drained aud a large part of it brought under
cultivation, but there is still 12 or 14 feet of peat at the N.W.
end. Men are still living who can remember this in the state of a
marshy pool, on which punts were employed in shooting wild fowl ;
this was drained in 1804 and the water taken under the embank-
ment of the Wilbraham river by means of a hollow trunk ; this
having become useless a brick tunnel was made in 1863, and the
drainage level at that time was found to be 6 feet below that
marked by the old trunk ; the level of the fen had sunk, therefore,
6 feet in about 60 years.

The bottoms of the (usually dry) valleys which drain o£P the higher slopes of
the Chalk hills are often occupied by gravelly soil or rainwash to a depth of
some feet ; thus in the valley runninf^ northward from Balsham there is a
deposit of dirty gravel and sand extending from Wadley Hall in a narrow strip
beyond Larks Hall, which has probably been form£d to a great extent from
the waste of older river gravels once existing at higher levels.

Similar deposits occur in Westley Bottom to the north, and there assume the
character and importance of actual river-gravel ; they flank the N.E. side of
the older gravel-ridge for some distance, but die out beyond Bottisham Heath
Farm. Small pits have been opened at several spots, and show 4 or 5 feet of
soft sand or sandy gravel. Their origin is doubtless to be found in the detri-
tion of the older gravels by rain and floods.

Valley oj the Ouse, Higher Terrace.

The valley gravels of that small portion of the Ouse which
traverses our area occur in two terraces, the same as those
described in the several channels of the Cam system. The older
occupy plateaux a few feet only above the level of the alluvium,
but are cut off from it and from the more recent deposits of gravel
at a lower level by a narrow outcrop of Oxford Clay. There is
but one exception, and this may be more apparent than real ; a
large patch N. of Somersham, which is evidently part of the
higher terrace, at and near that village, but seems to pass without a
break down to the fen, and is so mapped as no clay occurs between ;
either the two terraces are close together at the northern end and
a sandy wash between obscures the division, or there is but one)Q|^

110 GEOLOGY OP Tnp NEIGHBOURHOOD OF CAMBRIDGE.

terrace (the higher) and a wash from this runs down the gentle
slope to the fen, and entirely obliterates the real boundary.

On the right bank of the river there is but one spread of this gravel (unless
that at Over should prove not to belong to the ancient river .series); it is,
however, of good size, two miles lonfr and nearly a mile broad, extending from
Fennv Stanton to Fenny Drayton. The gravel has been dug in several places,
but the only good section is in the pit half a mile S.E. of Fenny Stanton,
which is 5 feet deep in fine very chalky gravel, with patches of false-bedded
light-coloured sand and loam, the beds contorted.

On the opposite bank of the river a similar outlier of gravel occurs capping:
the higher ground, forming an excellent site for the villages of Holywell
and Needingworth. Its southern end comes close to the marsh, but the pank
is steep, so that the base of the gravel is at least 10 feet above the surface of the
alluvium. There are many pits in this gravel, especially at Needingworth ; at
one, just W. of Holywell Church, there is a depth of 7 feet of fine subangular
gravel, with thin bands of sand, and a line stained by oxide of manganese, and
similar gravel occurs with brown sand in the pits on the eastern side of the
church. At a pit near the cross roads in the village of Needingworth there is
fine subangular gravel, mostly of flint with some quartzites, to a depth of 9
or 10 feet, with sand and water at the bottom. Gravel of the same description
is seen in a pit just £. of the village.

The villages of Colne and Bluntisham stand partly on the next patch of
gravel at this level; it is of the same description, but is exposed in few sections ;
a small pit in the farmyard, E. of Colne Church showed several feet of good
gravel.

A smaller patch is that on which Colne Windmill is situated ; a small pit
in this, just S. of the Somersham Railway Station shows 2i feet of brown
angular gravel.

Another large spread of gravel, 2 miles long and a mile broad, comes on
northward firom Somersham Station, and is traversed along its whole length
by the St. Ives and March Railway. The gravel is exposed in the cuttings, but
is best seen in the many pits in and around the village of Somersham. It is
interesting from having yielded a fine skull of Bos primigenius, with horns
attached, which has been placed in the Geological Museum at Jermyn Street
through the kindness of Mr. Robert Hemsted, who had obtained it from the
workmen. We recovered a jaw, two tibia, and several other bones of the same
animal from the bone merchant who had purchased them &om an itinerant
dealer in such wares. This dealer had bought from the gravel-diggers a barrow-
load of these bones for 6d, ; but we could recover only about a dozen out of a
huge heap which he was good enough to have picked over for the express pur-
pose.

A section in Somersham Station-Yard, shows 4 feet of brown angular gravel,
and some pits just N. of the station gave the following section : —

Feet.
Sandy soil « - - - - - -3

Fine angular stratified flint gravel - - - - 3J

Yellow Sand, said to be about - - - - 3

Oxford Clay, said to have been reached at a depth of - 15
Other pits a quarter of a mile N. of the church show —

Sandy soil - - "." " " "^

Fine angular stratified gravel, with patches of sand and

loam - - - " - - "8

Grey loam and water.
The skull and horns of Bos primigenius were taken in 1877 from the base of
this gravel. One of the workmen stated that some years ago a similar lot of
bones was found in the .pit, also a stone " battleaxe," and that these were
sent up to some London Museum.

The small island of Oxford Clay in High North Fen, in which Rumbold
Farm stands, is capped by a patch of gravel, small in extent and thickness.

Valley of the Ouse, Lower Terrace.

ITie town of St. Ives stands on abroad spread of this deposit, which occupies
both banks of the river. We have no measurement of its thickness, but it is

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POST-aLACIAL DRIFT. Ill

doubtless many feet, and it passes in under the alluvium. A mile S.W. of the
town a pit 5 feet deep, S.E. of the " Woolpack " Inn, shows it to consist of a fine
stratified gravel, with coarser gravel below, containing some large stones,
quartzites, &c. From this point the gravel may be expected to thicken con-
siderably towards the river, but the pits just south of St. Ives are in fine chalky
gravel to a depth of 3 feet only, when the water-level is reached, checking
further operations. There are numerous small pits on the northern bank of
the river, several ponds also expose the gravel, which supplies them with an
abundance of water.

Some small pits S.W. of Swavesey Church show 3 feet of fine brown angular
gravel and sand, and a similar gravel is exposed in some pits south and west
of Oxham Fen.

*' The Holcroffcs," north of Over, occupy another broad expanse of similar
gravel, which is seen in many ponds, ditches, and small pits, but the only
excavation of any importance is just N.E. of Over, where the pits show 4 feet
of fine angular gravel and sand. There are some old pits half a mile N.W. of
Willingham, where the gravel is exposed beneath a few inches of soil, consisting
entirely of decaying peat, in fact, the " feather-edge " of the Fen.

Over Court, on the left bank of the Ouse, stands on a patch of gravel
rising from beneath the Fen ; it is seen in a pit north of the road to
Holywell.

Bluntisham Fen is skirted on the west and north by banks of valley gravel.
A pit near the edge of the Fen, south of Bluntisham, was in fine angular gravel,
with horizontal lines of stratification, 5 feet deep. A small pit further east
shows 4 feet of similar gravel.

A pit, south of Bluntisham Church, was being worked in 1877 for ballast
for the new line of railway (St. Ives Extension), and gave an interesting sec-
tion 6 feet deep in fine sandy stratified gravel, with a layer of grey clay
(2 inches thick) in the middle, enclosing Bithinia tentacularis, CyrenafiumU
nalis, Pisidium, and Cardium edule. There is a thin layer of shell-marl near the
top of the gravel.

A small patch of valley gravel, or rather of wash from an older gravel, occurs
just north of Newmarket Union House, where a pit shows : —

Feet.
Brown sandy wash - - - - 2

Light-coloured sand - - - - 3

Flint gravel ;

and a well in the pit touches Chalk about 12 feet from the surface.

An old pit, a few chains N.W. of the Union House, is said to have been in
15 or 16 feet of sand.

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112 GEOLOGY OP THE NEIGHBOUBHOOD OF CAMBRIDGE.

CHAPTER X.-RECENT DEPOSITS.

Alluvium and Peat

There is little to be said regarding the alluvial soil which skirts
the banks of the several streams, for it is very seldom seen in
section. It usually, but not invariably, rests on gravel, and it
varies in depth from a few inches in the higher parts of the tribu-
tary valleys to several feet below Cambridge. Some observations
on the outlying area of Fulbourn and Wilbraham Fens have
already been given (p. 109.)

A good section was, however, seen in the western bank of Byron's pool, near
Grantchester, where the face, freshly cut by the floods in 1875, exhibited : —

Feet.
Black peaty soil - - - - - - -1

Layer of black mud with stones at the base, fragments of deer-
horn and many shells, such as Jbimnea stagnalis, Bithinia tentacu-
lata, Planorbis complanatus, Paludina Ldsteri, and ifnio pictorum 2
Loose gravel, 2 or 3 feet shown.

North of this, hj Grantchester and Cambridge, the alluvium appears to be
everywhere underlaid by gravel, but opposite Fen Ditton the river has cut a
more recent channel for itseJf through the Chalk Marl, and the outcrop of the
Cambridge Greensand would probably be found under the alluvium about
half a mile N.N.W. of Fen Ditton Church.

Beyond this point the alluvium widens out by Milton Fen and Clay Hithe,
and finally passes into the broad expanse of the feus towards Upware. On
the west these fens run back southward toward Homingsey, Quy-cum-Stow,
and Swaffham Bulbeck, but the depth of peat is nowhere very great over these
inlets of the fen country, and there is sometimes little more than a turfy soil.

Along the edges of the fen the turf generally rests directly upon Gault or
Chalk Marl, as the case may be, but in the deeper portions it is often under-
laid by sand or sandy gravel. A strip of such gravel runs under the fen from
the neighbourhood of Horningsey north-westward, and may possibly mark the
prolongation of the old channel of the Quy-water stream. Again, in SwafPham
Bulbeck Fen there is sand or silt in some places, and the following section was
seen in a pit near the junction of the *' Black " and " White Droveways."

Feet.
Black peaty soil - - - - 1

Fine yellow sandy silt - - - - 4

Chalk Marl, about - - . . - 7

At the other end of the Black Droveway the peaty soil is very full of land
and fresh water shells, amongst which Cyclostoma elegans is common. This
shell also occurs in the Warp, but is not, to our knowledge, found alive now
in any part of Cambridgeshire. Helix lapicida also occurs at the same spot,
but is now very rare in the neighbourhood.

To the northward, in Reach and BurweU Fens, the peat is thicker, and is
still dug for fuel in many places.

Remains of prehistoric man, in the shape of flint implements of various
kinds, are frequently met with in these fens, and many are described in
Mr. Evans' " Stonejmplements of Great Britain.'? Flint and greenstone celts,
"with the sides more or less flat, so as to range between Figs. 53 and 58 (op.
dt.) are of not uncommon occurrence in the Fen country." Rough-hewn
flint celts are also not unfrequently found (op, cit,, pp. 61 and 68).

It may not be generally known, but it is a fact worthy of record,
that cattle left to graze for any time on the fen lands are liable to

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RECENT DEPOSITS. 113

a peculiar disease of the throat, termed ^' ulcers," the remedy for
which is removal to higher ground. It is considered, and with
much show of reason, that the attacks are induced by some noxious
ingredient of the water the cattle consume ; this drains into the
ditches and ponds from -the saturated peat, and must be more or
less contaminated by organic matter in a state of decomposition.

On this subject Mr. Jbnyns has some interesting observations. He says*: —
There is still an abundance of decomposing vegetation in those parts of the
Cambridgeshire fens which have not yet been brought under cultivation.
Portions of the fen remain unenclosed, and are purposely kept in a partially
undrained state for the sake of the peat or turf, as it is locally called, which
is dug out in large quantities for firing, and to which the poor in some
parishes have a common right. Wherever this is the case the moor is
broken up into a number of pits, that speedily become filled with water and
aquatic plants. Among the latter are certain species of Chara and Potama-
geton, which abound more than any others, and the first of these especially
is well adapted for causing a rapid accumulation of vegetable remains at the
bottom of the pits, by the constant decaying of the lower part of its stem,
while its upper extremity continues to make fresh shoots. From this cir-
cumstance there is soon formed a decomposing mass which, as the heat of
summer partially dries up the water, is exposed to the atmosphere, emitting
a most offensive effluvium. I believe these to be the plants whichj during
the putrefactive process, mainly contribute to the miasma that arises from

the Cambridgeshire fens The peculiar strong odour caused by the

decomposing Chara in the deeper pits is very obvious on approaching one
in sunmier that is half dried up. . . . This evil, however, is probably yearly
becoming less. All the best turf in Swaffham Fen has long since been used
up. What is now dug there is of a very inferior quality, and much less
profitable for fuel, and from the extent to which drainage has been carried
on in recent times the formation of new turf is no longer possible. The
time is probably not far distant when the whole moor will altogether cease
to be worked for turf, and when it will be found more to the advantage of
the owners to have it thoroughly drained and brought under cultivation,"

Warp cmd Trail,

This term, proposed by the late Mr. Trimmee, may perhaps be
taken as a convenient name for the soil immediately underlying the
vegetable mould. Mr. Trimmer says : — " The majority of the soils
and subsoils in the British Isles are composed only in part of the
debris of the rocks on which they rest, and in part of materials
transported from various distances;" the soil thus produced he
calls the " warp," or the " w^urp of the drift.*'

It appears to us that Mr, Trimmer would have included under
this name that portion which Mr. Fisher subsequently separated
under the designation of *^ trail." We are inclined, therefore, to
define warp as comprising all the material between the vegetable
mould and the undisturbed subsoil or rock forming the underlying
stratum. This would include most cases of trail and rainwash, as
well as ordinary soils, which often, as Mr. Fisher has pointed out,
extend underneath the peaty or silty clay of alluvial flats.

The depth of such Warp varies, of course, very greatly, but we
have not seen any instances in Cambridgeshire where it was more
than 5 feet.

* Observations in Meteorology, London, 1858, p. 374 ; see also the same author
" On the Turf of the Cambridgeshire Fens." Iiep» BriU Assoc, for 1845, Section 5,
p. 75.

f Quart, Joum, GeoL Soc,, vol. xxii. p. 562.

N309. H

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114 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBBIDGE.

A good instance of such warp or wash was seen in a trench opened for
obtaining coprolites near the river half a mile N.N.W. of Harston, the section
being as follows : —

Feet.
Dark grey soil, about . . • • « 1

Compacted marly silt^ probably rainwash from the hill to
the west - - - - - -3to4

Fine river gravel - - - - -lto2

Bedded clunch^ in place - - - - 8 ?

Mr. Fisher, in describing the soil overlying the clunch in the pits between
Harlton and Haslingfield, says* : — '* The upper portion of the sections usually
exhibits from a foot to a foot and a half of soil, which I call, after Mr.
Trimmer, Warp, In this district it is unusually full of land shells of recent
species. Nevertheless the assemblage is not exactly what one meets with
hving on the spot." He instances Cyclostoma elegans as veiy common in
the Warp, but not found alive, also H. arbustorum as the commonest Helix in
the Warp, while now H, nemoralis is commoner, and he thinks it likely that
drainage and cultivation may have been sufficient to have caused these changes.

Below the warp in these pits is found the marly clay with stones and patches
of gravel, which Mr. Fisher calls "trail;" this is without shells, is com-
parable to the rainwash in the above section, and its average thickness
appears to be from 2 to 3 feet.

* GeoL Mag., vol. viii. p. 65.

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DRIFT. — THEORETICAL CONSIDERATIONS. 116

CHAPTER XI.

Theoretical Considerations as to the Physical Conditions

UNDER WHICH THE GlACIAL AND PoST-GlACIAL DrIFTS
WERE DEPOSITED.

I. Bovlder Clay.

Having described the various drift deposits in our district we
may now oflFer some remarks on the conditions under which they
were formed, and may state the conclusions to which we have
been led from the study of their structure and mode of occurrence.

There is no doubt that the Chalk, covered by Eocene beds, once
extended over and far beyond the area of the map (PI. 7), although
within its limits not a vestige of the latter now remains.

Professor Ramsay believes that the Seoern, after Miocene times,
''began to ci»..t a valley towards what afterwards became the Bristol
Channel, and estabhshed the beginning of the escarpment of the
Chalk; which has since gradually receded, chiefly by atmospheric
waste, so far to the east If this be so, then the origin of the
valley of the Severn (i.^., the 'beginning of the escarpment') is of
immediate Post-Miocene date."*

The escarpment probably had receded to its present position,
or thereabouts, by the end of the Pliocene period. During the
progress of the partial Eocene submergence and the subsequent
re-elevation, the Chalk was subjected to some disturbance, re-
sulting in the formation of mai;iy small faults, flexures, and contor-
tions. A considerable flexure of this or a later period probably
gave rise, as we have seen, to the formation of the coomb-like
hollow, called Wardington Bottom, which now forms an upper
extremity of the Cambridge Valley (see p. 83).

Although the escarpment had been cut back to its present posi-
tion by the close of the Pliocene period, and the land was somewhat
submerged during the deposition of the Pliocene beds on the east
coast, there are in our area no signs of their present or former
existence. For the valleys were not excavated to their present
depth by perhaps 50 or 100 feet, and consequently any such
deposits that may have been formed therein have long been swept
away. For the same reason there are no deposits which can be
referred to the earliest part of the succeeding Glacial period ; it
is, in fact, doubtful whether any were formed within the area.
For these may have been excluded from the district by its then
height relatively to that at which they occur elsewhere. Indeed
we are now inclined to think that the Chalk hills were nearly or
quite continuous across the Wash during Pliocene and early
Pleistocene times, and that this barrier was not broken through
until the period of the Upper Glacial Clay.

Neither, with two j)ossible exceptions (see p. 73), do we find
any of the so-called Middle Glacial deposits, which just over the

* " Physical Geology of Great Britain," Ed. 3, p. 219.

H 2

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116 GEOLOGY OF THE NEIGHBOURHOOD OF OAMBBIDGE.

Chalk escarpment run up to a height of 300 feet or more above
the sea, and to at least 200 feet above what must have been the
bottom of the Cambridge Valley at the time of their deposition.
Had such beds been formed we should expect to find them still
between the older rocks and the Boulder Clay, at least in some
part of the area within which the latter occurs. It cannot be
assumed, as in the case of the Pliocene beds that the " Middle
Glacial " beds at one time occupied the valley, and were after-
wards (but before the Boulder Clay period) removed ; yet in no
instance do we find the Boulder Clay resting on any other than
Pre-glacial formations. This question has already been discussed
by one of us, and an explanation of the probable causes which
excluded the Lower and Middle Glacial deposits from the Cam-
bridge Valley given in a paner on " East Anglia during the Glacial
Period."*

As we have seen (p. 77) the Boulder Clay rests, or has rested,
on a surface of older rocks corresponding very nearly vrith that
which now forms the Cambridge Valley, this old surface having
been covered by the deposit. As the clay occurs from the lowest
to the highest point, the question naturally arises has this old
valley been completely filled by a great thickness of Boulder Clay
since removed by detrition ? We think not, but that the clay
was of fairly uniform but not great thickness, perhaps 100 feet or
thereabouts, from the ground now occupied by the fens up to and
over the Chalk escarpment. The formation of such a sheet of
material, spreading alike over hill and valley, involves, we are
aware, the existence of conditions very different from those under
which extensive deposits are commonly formed.

The total absence of all signs of stratification justifies the ex-
clusion of the ordinary conditions of deposit from water ; but we
think it shuts out also the theory sometimes advanced of the entire
mass of the clay having been dropped from melting bergs of ice.
Such hypothesis demands that the clay shall have been ground up
into its present unstratified condition, and have received its
heterogeneous constituents elsewhere ; and, to a limited extent,
this has been the case, but the theory of accumulation by ice-
bergs does not explain how or whence the material was derived.
Further, we are satisfied that any finely divided matter, so dropped
from floating icebergs, whether in small or large masses, could not
fail to exhibit fine or coarse lines of rude stratification.

It has been forcibly urged that such a clay could and would be
formed beneath a sheet of land-ice, and that it would necessarily
consist of a mixture of the debris of the various rocks over which
the ice-sheet had ground its way. And the fact of the Boulder
clajr being, to a great extent, everywhere composed of the worked-
up ingredients of the formation upon which it rests, lends great
apparent support to this solution of the problem ; but it has never
been shown (so far as we are aware) that a sheet of land-ice does
form beneath itself a thick bed of re-assorted material ; examples
from ice-covered countries of the present day have not been quoted
m evidence. On the contrary, it has been observed that where
large sheets of ice exist they denude rather than cover up the

* Penning, Quart. Joum. GeoL Soc, vol. xxzii. p. 191.

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DEIFT. — THEORETICAL CONSIDERATIONS, 117

floor over which they pass and their smoothed and striated beds
are rather cited as marks of ice-action. Of course if an ice-sheet
erodes the underlying rock, the material resulting from this
detrition must be re-deposited elsewhere ; but it is impossible that a
sheet of ice should both wear away and cover up a surface at the
same time. It has been suggested that such detritus would
be re-deposited in the hollows of the surface, while the higher
points would alone be striated and ground down ; but if such had
been the origin of the Boulder Clay, high and low ground alike
woidd not have been covered by a thick mass of the deposit.

Moreover, it is necessary in seeking an explanation of the origin
of this clay to account for the presence in it of boulders of rock
derived from a great distance. This can scarcely be ascribed,
considering the local character of the clay, to the passage of ice
over the land between their original site and present resting place.
It is due rather to the work of ice-floes or icebergs, although, for
the reasons given above, we cannot accept the idea of the clay
having been altogether transported and formed by their agency.

We see that the Boulder Clay has been ground up into its present
unstratified condition, and has received its heterogeneous ingredients
through some kind of ice-action ; also that it is^ to a great extent,
everywhere composed of the worked-up constituents of the forma-
tion upon which it rests. B\it, for the reasons advanced, we are
not prepared to adopt either of the hypotheses above-mentioned,
and we venture to suggest that neither will, at least in this area,
be found to account satisfactorily for the phenomena.*

** There is, however," as Professor]John Milne has truly said, " another form
of ice, which, from its unassuming appearance, although touched on by a few,
has apparently taken too low a place in the role of actors with which it plays
.... this is coast-ice.'*

" From what I have seen of coast-ice and of its effects, I feel persuaded that
it is an agent of at least as great, if not of greater, universality than either
glaciers or icebergs, and taken as a whole perhaps also as an agent of equal
power. Of the various forms of sea-ice known as ' berg-ice,' ' floe-ice,'
* park-ice,' and the like, the portion I would more particularly draw attention
to is that variety which forms a narrow belt along the shore, known in Green-
land as the ' ice-foot.' "

" It would appear that in the formation of the ice-foot, we may

have either one or many causes called into operation The ice-foot

of Greenland owes its origin to the action of the tides The first

frost of the late summer covers the sea with a crust of ice, which, carried
upwards along the face of the cliff by the tide, eventually becomes glued to
the rocks. It thus grows in thickness with every successive tide until it
may reach a height of 30 feet, and sometimes even more, presenting to the
sea a bold wall of ice against which the floes grind and crush."

" The blasts of December and January drive the spray high up upon the
land, and there it freezes as a cake of ice; day after day and night after
flight this continues, and the crust grows thicker . . . until at last it is from 2
to 3 feet in thickness. Stones of all sizes, from pebbles to boulders, on
which this coating may rest, are now firmly set in an icy maw of ice, and
are ready at the first moment to cut and grind a path for themselves.

" This generally goes on until some portion of the northern pack, coming
south, meets with an adverse wind and is driven ashore. When we reflect
upon the immense mass contained in one of these moving fields of ice, we

* Geol. Mag., Dec. ii., vol. iii. pp. 304 and 403. See also a paper by the same
author, ** On the Action of Coast-Ice on an Oscillatiiie: Area.'* Quart, Joum, GeoU
Soc.^ vol, xxxiii. pp. 929-31 (1877). *

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118 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBRIDGE.

can hardly conceive the energy that is stored within it. Everything has
to give way hefope it, and the coast-ice, with its set of gravers firmly bedded
in its base, is pushed high and dry, sometimes as much as 100 yards^ back
from high-water mark. It is in this wav, by the coming in of the northern
pack, the rise and fall of the tide, and otner causes, that the land-ice is driven
ashore, and many of the scratches and grooves so common round the coast of
Newfoundland have been made."

'* In addition to the work done in scratching and grooving by the coast-ice,
it also does much in the transportation of material. When in deep water,
chafing along the face of a cliff by its own horizontal and vertical movements,
together with its continued force of impact on a heaving swell, it must detach
a considerable amount of material. Tnis, together with that which may fall
upon its edge from the rocks above, is carried by the coast-ice to a new home.

"The chief agent, however, in the transportation of material's the ice-foot
attached to the shore. At low water this freezes to the ground on a shehang
shore, and is at once firmly attached to both boulders and stones ; when the
tide rises this ice, with its cargo, floats and may be carried away. The
consequence of these transportive movements is that much material, both
boulders and pebbles, are carried out to sea, and then deposited in a manner
similar to that which has so often been explained in the case of icebergs.
Another consequence is that similar materials are carried from point to point
along the coast, and on the disappearance of the ice are left as monuments of
its former existence."

" The vast ice-fields which break loose from the frozen regions of the north,
and we read of them 300,000 square miles in extent and 7 feet in thick-
ness, are, in their passage south, driven in upon the land, and help to grind

the coast line and transport its boulders Amongst the inhabitants of

Newfoundland the action of coast-ice as a transporting agent is universally
recognised, whilst ice bergs in the same latitudes are seldom seen with earthy
materials upon them."

Speaking of the ** ice-foot " in Greenland, Dr. R. Brown says : — *

" As the spring and summer thaws proceed land-slips occur, and earth,
gravel, and avalanches of stones come thundering down on the ice-foot, there
to remain until it breaks ofiP from the coast and floats out to sea with its raft-
like load of land debris. As the summer's long sunlight goes on, the ice worn
by the sea parts with its load ; and this may be shortly after its leaving the

land, or it m&y float tolerably far south Often fields of ice will float

along and, like icebergs, graze the surface of rocks only awash at low tides,
and therefore its action might be mistaken for that of icebergs or land-ice. In
other cases I have known the ice-foot, laden with debris, to be driven up by the
wind and high tides on to low-lying islands, spits, and shores, pihng them
with the load thus carried from distant localities.

Again, speaking of ground-ice, which is formed below shallow water on the
bottom of the sea, he states that it " often rises to the surface laden with sand,
gravel, stones, and seaweed. Sheets of ice, with included boulders, are
driven up on the coasts during storms and packed to a height of 50 feet.
How easily such sheets of ice, with included sand, gravel, or boulders, may
furrow and streak rocks beneath may be imagined."

Lastly, we would adduce the testimony of Prof. Youle Hinde, who has
described the extensive formation of Boulder Clay on the north-east coast of
Labrador through the agency of " pan ice," which is derived from bay-ice,
floes, and coast-ice ; " thus broken ice is pressed on the coast by winds, and
the pans rise over all the low-lying parts of the islands, grinding and polishing
exposed shores, .... the masses pushed or torn from these surfaces are
urged into the sea and rounded into boulder forms by the rasping and
pohshing pans."t

The foregoing extracts have been reprinted because we are con-
vinced that the agencies therein described are exactly similar to

* Physics of Arctic Ice. Quart, Joum. Geol. Soc, vol. xxvi. p. 689.
t Notes on some Geological Features of the N.E. Coast of Labrador. Canadian
Naturalist, vol. viii.

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DBIFT. — THEOBETIOAL CONSIDERATIONS. 119

those by which the Great Chalky Boulder Clay of East Anglia was
chiefly produced.

The arguments by which we consider the coast-ice theory can
be mainly supported are : — (1) The great extent of coast-ice as
compared with that of glaciers. *' Looking at the Northern Hemi-
sphere only, and comparing all the deeply-indented coast-lines
(say that of North America and Greenland, every yard of which is
more or less subject to the action of coast-ice) with the portions
throwing off glaciers to form bergs, it will be seen that the
coast-ice must in quantity be infinitely greater than the glaciers."*
Coast-ice is not only of greater extent, but it would act more
equally on every part of the coast where it occurs, although its
work would gradually decrease in the direction of warmer latitudes.
Any product of its action would consequently be more uniform in
thickness than that which is glacier-formed and berg-transported ;
for this must of necessity thin out in every direction from certain
maximum points of deposition. The Boulder Clay extends, or has
extended, over all the area where it now occurs in mass or in
patches, and was of fairly uniform thickness, which causes it to
conform so nearly as it does, on the large scale, to the contour-
lines of the district.

2. The great uniformity in the characteristics of the clay, which
varies as the nature of the deposit on which it reposes ; such
variations affording another proof of local, as opposed to distant, for-
mation. Wherever exposed the clay is seen to be unstratified,
and presents an appearance of having been rolled, jammed, or
beaten into its present state, rather than of having been dropped
from icebergs, for we might reasonably expect in such a case that
the clay would vary quickly according to the difference of the loads
deposited, derived from distant sources of formation. There would
also be lines of division, not to say stratification, between the
freights thus deposited ; but no such lines of division and no such
sudden changes of material have been observed.

It has been shown that even in this limited area the clay
simulates the formation beneath ; on the Oxford Clay it can be
distinguished from it only in actual section; on the Gault it
resembles Gault ; on the Chalk it is often nearly white in colour,
and is in fact reconstructed Chalk; but in each case it contains
boulders of chalk and of other rocks, all from the North ; not how-
ever as patches of Chalk, of Oolite, or of any other deposit, but
scattered throughout the mass. Whatever the origin of the clay,
the boulders enclosed in it must have been ice-transported (either
by themselves or within the mass of the clay) ; we assume that
they were brought by bergs to the area within which the clay
was being formed, and that they were afterwards incorporated as
component parts of the clay.

3. Fragments of rocks which occur within the area, but at a much
lower level, are now found at the higher points, even on the summit
of the Chalk escarpment. As an instance of this may be mentioned
the phosphatic nodules from the " Cambridge Greensand," which
were taken from Boulder Clajr on the high ground south of Royston
(see p. 75). This lifting of local fragments, which can be cer-

♦ Milne, op, cit, p. 408.

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120 GEOLOGY OF THE NEIGHBOURHOOD Or €AMBBIDGE.

tainly identified, to much higher ground in a comparatively short
distance is work that we conceive scarcely possible to any other
agent than coast-ice, acting in the manner previously described
(p. 117).

After careful consideration of the evi<lence, and a study of the
clay itself in very many sections, we are convinced that coast-ice
has been the main agent in its formation. This has ground down
and mixed up the material of the shores subjected to its action,
and incorporated with it other material brought by itself from some
near locality, or by icebergs from a distance. It has pounded up
the mass again and again, rounding the softer pebbles, but making
little impression on the harder ; and it has by repeated shillings
moved debris from the lowest to the highest points now under
consideration ; and it has been aided in this, it must be borne in
mind, by its work being done in a sinking area; every part of which
in turn was subjected to its influence. Nay, every part bos twice
been acted on by this agency, first as the land was sinking beneath,
and again as it emerged from, the waters of the Glacial Sea.

It may be supposed that as the land went down it would be
covered, as a sea-bottom, when once below the level of coast-ice
influence, with sand, gravel, or stratified clay. Possibly it was so,
but any deposits then formed on the surface of the earlier clay
would be removed and ground up with other material by coast ice
on its emergence. It may be that the beds of sand, gravel, or loam
here and there found associated with the clay are trifling represen-
tatives of such intermediate deposits, although few would escape,
considering how readily they must have yielded to such powerful
denuding agency.

After the completion of the M.S. of this memoir, our colleague
Mr. Skertchly (firstly in the Geological Survey Memoir on *' The
Geology of the Fenland," and then in *' The Fenland Past and
Presenv' by Miller and Skertchly) strongly advocated the theory
that the Boulder Clay was formed beneath land-ice. Notwithstand-
ing his assertions, however, we are still convinced that the argu-
ments in support of a coast-ice origin have the advantage.

We are pleased now to find that our views on the origin of the
East Anglian Boulder Clay are in accordance with those of our
Director-General Prof. Ramsay,* who quotes Prof. Youle Hind's
account of the action of *' pan-ice" (coastrice) and the formation
of Boulder Clay and observes that '* as the British Islands during the
Glacial epoch were more than once much in the same state as
the north of Labrador there can be little doubt that some of the
British phenomena were produced by the same causes."

2. Post-Glacial Gravels,

In this district we have no indications of the greatest depth of
the Glacial submergence, but it was probably many hundreds of
feet ; that it continued for a long period is certain, judging from
the thickness of the Boulder Clay. Whatever oscillations of level
may have occurred elsewhere during the Glacial period, there are
in our area marks of but one, and that a gradual long-continued

* See his " Physical Geology and Geography of Great Britain," Ed. 5. p. ^6

(1878).

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DBIFT. — THEORETICAL CONSIDERATIONS. 121

movement of depression, succeeded by an equally gradual re-
elevation.

When this re-elevation began, and as the land rose from beneath
the sea, every part in turn, as a receding shore-line, would be
subject to the action of the waves and of the ice-foot, the surface
of the newly-formed Boulder Clay being " thereby eroded and to
some extent re-assorted. A clayey gravel would naturally result,
and the whole of the uneven surface of the clay would be more or
less covered by such material " ;* but larger masses would be accu-
mulated on the flats and in the hollows and channels.

We consider the oldest gravels described (pp. 79-81) to belong to
this period of emergence, and that they were formed from the waste,
partly submarine and partlv subaerial, of the Boulder Clay. As the
land rose these deposits advanced their edge, constantly following
and infringing on the receding zone under the influence of coast-ice,
which was, however, at that time much diminished in extent and
importance.

As the elevation of the land continued, and when a considerable
area had risen above the waves, the action of subaerial agencies
would be intensified, so that the detrition of the higher ground
would be usually rapid. This detrition was indeed of no ordinary
character ; extensive denudation was the result, and this has oven
been taken to indicate a period of excessive rainfall, resulting
in the formation of deposits equally abnormal in their development.
Mr. A. Tylor has suggested that this should be called the
"Pluvial Period,"t and he believes that during this time there
were such great land-floods that the previously existing valleys were
entirely filled up with beds of gravel, and loam washed in from the
high ground along their sides ; he further considers that the present
rivers have only re-excavated their courses through the immense
mass of material thus accumulated.

Prof. Prestwich too has called in the agency of floods to account
for some of the appearances presented by the series to which he
gives the name of high-level gravels, and other observers have come
to like conclusions.

Mr. Skertchly has described gravel on the edge of the Fen-
land, which he considers to be '* a deposit formed by land-floods
during excessive rain, which swept over the country irrespective
of its natural features, and after those features were n)rmed.
**The deposit," he says, '*is essentially of local origin, as is shown
by the ingredients which constitute its mass, and seems to have
been formed during intense floods."! He therefore terms it
Flood Gravel," and refers to this deposit the gravels which cover
the high ground between the valleys of the Little Ouse and the
Lark, and which appear to occupy the same position as the gravels
we have mapped south of the Lark Valley.

There are evident objections to invoking the agency of abnormal
conditions, when those which already exist are equal to the per-

♦ See " East Anglia during the Glacial Period," Quart, Joum. Geol. Soc, vol.
xxxii. p. 195; also "The Post Tertiary Deposits of Cambridgeshire." Cambridge
(1878).

t Quart Joum, GeoL Soc,, vol. xxiv. pp. 105 and 455, and xxv. p. 58.

t The Geology of the Fenland, pp. 195, 208. Geological Survey Memoir, 1877.

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122 GEOLOGY OF THE NEIGHBOUEHOOD OF CAMBBIDGE.

formance of the work ; still we admit that the unusual characters
and positions of these deposits point to a peculiar combination of
conditions at the period when they were formed. We hope, how-
ever, to show that the rainfall of that time need not have been
excessive, and to account not only for the torrential action which
led to the formation of these so-called " flood gravels," and con-
tinued during the deposition of the old river gravels, but also for
its comparatively sudden cessation.

We have suggested that the Boulder Clay did not entirely fill
the Cambridge Valley, which would have involved a thickness of
at least 400 feet over the low ground. On the other hand we
think that the land sank, and that the clay was formed along the
margin of the sinking area at a fairly uniform rate, resulting in a
sheet of the material, which wrapped over high and low ground
alike, except at the highest pomts of the escarpment S.W. of
the Cambridge area. The old larger features were thus preserved,
minor hollows were of course filled up, but the larger valleys, as
such, still existed on the emergence of the land. This being so,
it matters not what might have been the actual thickness of the
clay, 5 feet, 50 or 100, the result would have been much the same—
the rising ground on the north, the escarpment on the south,
the low ground between, would all have been covered by a sheet
of impervious Boulder Clay.

What would take place now, with our present rainfall on an
area so situated ? We cannot quote an exactly analogous case ;
but where high clay lands are found the streams are quickly filled
in rainy seasons, and unless the channels are kept in good order
the low lands are soon inundated. Those who live on the western
borders of the Fen have nothing to fear from the Fen waters, but
after heavy storms the water from the high lands rushes down, and
thus their lands are "drowned." In a district such as this must
have been just after emergence from the Glacial sea, with a con-
tinuous covering of impervious clay^ all the rain falUng on the
higher lands would make its way quickly to lower levels. The
whole rainfall would thus be rapidly collected in the then
existing channels, a large body of water therefore would flow along
and erode them, producing all the results which have been attributed
to excessive rainfall.

In times of rain and storm these streams would quickly rise and
flood their banks, producing wide-spread deposits over what were
then the lowest grounds, but which are now, through later denu-
dation, many feet above the present alluvial levels. Some of these
deposits might therefore be correctly termed "flood gravels," but
we do not believe that beds formed in this way were ever so ex-
tensive as to " spread all over the country, crossing water-sheds,
occupying the highest ground and running down to the lowest"*
We cannot but think that when the country has been completely
mapped, it will be found that gravels of two or more ages have
here been treated as contemporaneous.

While fully prepared to admit the cogency of the evidence
brought forward regarding the great volume and velocity of the
ancient rivers, in this and in other parts of England, we cannot

* Skektciily, in J. Geikie's " Great Ice Age," Ed. 2.

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DBIFT. — THEOBETICAI. CONSIDEBATIONS. 123

regard this as any proof of a proportionately great rainfall ; we
believe, in fact, that a Fluvial Period need not necessarily be a
Pluvial Period. Especially we hope to explain the causes by
which the present order of things was brought about, and the
chief effect of which was the cessation of the undoubted torrential
action.

3. The Physical History and Relatwe Ages of the Biver Valleys,

We now proceed to consider the physical conditions which pre-
vailed in Cambridgeshire during the formation of those gravels
which are distinctly of fluviatile origin.

Reviewing the facts brought forward in the preceding pages, regarding the
disposition of these river gravels, we may draw some conclusions which have
an important bearing on certain points in the physical geology of the Cam
Valley, and may gain some idea of the succession of changes which have
taken place in the countiy since the Glacial Period.

It has already been pointed out that the earliest series of loams and gravels
in the district, bear witness to the existence of a river-system quite different
from the present, and entirely independent of the existing lines of drainage,
except in the uppermost parts of the tributary valleys descending from the
Chalk Hills. As we trace the oldest series towards the hills, we find that the
direction of its branches gradually approximates to that of the present
valleys, and that these old river deposits have a recognizable relation to the
ultimate valleys and coombs of the Chalk escarpment.

We conclude, therefore, that the outline of the hill districts has not changed
within the Recent period so much as that of the lower country, and the plains
beyond ; that the valleys which now furrow the sides of the chalk hills may
be regarded as the ends of the old valleys formed by these ancient rivers, more
deeply worn it is true, but still following the original lines. In the lower
country great changes have taken place, and an immense quantity of material
has been removed by denudation, so that the deposits which once lay in
valley bottoms are now found along the ridge tops, and are sometimes cut
through by channels of more recent origin, not only so, but it would appear
that in one part of the Cam Valley (between Whittlesford and Cambridge)
the destruction of ground by the combined action of rain and rivers has been
so great thak all traces of these ancient deposits have been swept away.

We are now brought face to face with the question. What caused this altera-
tion in the general system of drainage, or in other words. Why have the tributary
streams of the Cam deserted the courses which were taken by two of the main
affluents of the older river?, that from Wardington Bottom, and that from the
neighbourhood of Wilbraham. We must conclude either that there is a con-
siderable period of unrepresented time between the epoch of these ancient
rivers and that marked by the formation of the Barnwell and Trumpington
series of gravels, or that there are facts which will explain this apparent break
without having recoiurse to such a supposition.

Let us endeavour to picture the country as it probably appeared at the
earlier epoch, and to reclothe its surface with those portions of the once con-
tintwus envelopes which have since been stripped away by denuding agencies.
We have reason to suppose that at the commencement of this terres&ial period
the mantle of Boulder Clay covered a far greater surface than it does now,
and must then have spread far more generally over the ground between the
Chalk scarp and the high plateau west of the Cam Valley.

At the time when the water ran along the older lines of drainage, we think
that the Gault was not exposed in any part of this valley south of Cambridge,
the river Rhee had not yet come into existence, ana the Orwell hills, with
their capping of Boulder Clay, stretched southwards to Shepreth and
Melboum, the water from their slopes flowing chiefly into the Wardington
Valley.

The general direction of the Bourn Valley may have been sketched out at
this early period, but looking to the position of the later ^vels along the
Barton and Grantchester ridge, the surface of the Gault can hardly have been
exposed here at any earlier epoch than that to which these gravels oelong.

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124 GEOLOGY OP THE NEIGHBOUEHOOD OF CAMBRIDGE.

The point at which the ancient iipravel series first impinces upon the surface
of the Gault is near Gravel-hill Farm, west of Cambriafj^e, and though the
southern branch of the river may have cut down to the Gault about St. John's
Farm, it is not likely to have done so more to the south. Lower Chalk, capped
by outliers of Boulder Clay, then covered the sites of Trumpinf(ton, Shelford,
and Harston ; the few springs then existing could not have been like those
now thrown out in the Lower Chalk, but were in different positions, and were
of necessity much weaker, the river being mainly supplied by water flowing
off the hills along the channels which we have already indicated.

It has already been pointed out that as long as the slopes above these
valleys were covered with Boulder Clay, a very large proportion of the rainfall
would be carried off along the siirface ; consequently the volume of the rivers
would then have been far greater than that of the present streams, and espe-
cially during seasons of flood : but as denudation proceeded the area of bare
Chalk would be much larger, and a proportionally greater quantity of rains
absorbed into the ground, to be partially thrown out again as springs when
it had reached a much lower level.

What would be the result of this greater absorption of the rainfall as
the Boulder Clay was gradually cut back to the slopes of the higher ground,
and a larger area of bare Chalk exposed? The effect on the system of
drainage would be two-fold: — (1.) Less water would flow directly into the
old channels, and thus the rivers would gradually lose their power to keep
those channels open ; (2.) The water absorbed by the Chalk would be thrown
out again in springs, and as these springs increased in volume their position
would greatly affect the courses ana directions of the streams.

We believe, therefore, that it was this important alteration in the absorp-
tion of the rainfall which produced the first great change in the direction
of the main lines of drainage ; also that the alteration in the position of the
springs, consequent upon their recession and the gradual lowering of the line
of saturation under the Chalk hills, was the principal cause of the subsequent
changes in the course of the Cam and its tributaries.

It is probable that on the outer slopes of the Gog-Magog Hills there were
in early times but two strong springs, where now there are four, and that the
position of the one was somewhere between the Nine Wells and the Cherry
Hinton spring (probably about the site of the Cambridge Railway Station),
while that of the other, represented now by the Fulbourn and Wilbraham
springs, was somewhere north of Fulbourn. It is a significant fact that the
probable positions of these two springs are opposite two gaps in the ancient
gravel-ridge, through which run two lines of more recent river deposits. As
regards the gap at Quy-water Bridges its probable mode of formation is pointed
out in the description of Wilbraham and Fulbourn Fens (p. 108), and there
can be little doubt that the process there indicated was only a repetition of
what had taken place over the site of Cambridge at a much earlier date.

As the old river firom the east declined in volume and strength, the power
of the springs proportionally increased, and changes occurred in the valley of
the river from the south, which was ultimately diverted into the channel
marked out by the gravels of the Barnwell series. The waters of what we
may call the Gog-Magog spring would be intercepted by this stream, and
the result would be the formation of a lake or lake-like expansion of the
river as in the cases of the Wilbraham (p. 108) and Hauxton (p. 105) lakes.

We have evidence of such lacustrine conditions in the character of the
deposits at Barnwell ; the loamy marl bed, (with its plant remains, its many
land and fresh water shells, and its well preserved mammalian bones) is the
slowly accumulated deposit of a quiet expanse of water, the home of Chara
and delicate molluscs, and the drinking place of elephants and other beasts :
moreover, the succeeding beds of sand and marl, with like contents, bear
witness to the continuance of like conditions for a considerable time. Gra-
dually, however, the lake silted up, and its overflow slowly worked a wider gap
through the obstructing ridge in front ; eventually, when the Chalk had been
worn through and the Gault exposed, erosion would be more easy and rapid,
so that the river has since continued to flow through the gap thus made between
Barnwell and Castle Hill.

In the outspread of loam, sand, and gravel about Histon and Impington we
have evidence of another lake-like expansion of this river where it was blocked

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DRIFT. — THEOBETIOAIi CONSIDERATIONS. 125

by the ridge of the Lower Greensand. Deflected north-eastward by this it
seems to have flowed by Landbeach and Denny Abbey towards Thetford and
Ely, where it may have entered the ancient bay of the Wash.

The subsequent changes in the valley south of Cambridge appear to have
been brought about by the tendency of all rivers in wide valleys to alter their
channels^ influenced in this case by the changes in the position of the springs
as their points of outflow were shifted farther back. Some of the episodes
which occurred during this period, represented by the intermediate series of
gravels, have been recorded in the description of these deposits (p. 101) ; we
now confine ourselves to tracing more fully the history of the Rhee Valley.

The origin of this valley, i.e., the cause that determined the existence of the
hollow which subsequently became a valley, was probably the existence of a
strong spring thrown out at the base of the Totternhoe Stone, when its outcrop
lay over the present site of Harston. As this spring receded southwards, a
valley began to be formed which received the drainage of the surrounding
hills ; minor springs from the horizon of the Melbourn Rock likewise came
into existence along its sides, and determined the position of tributary water-
courses. The strongest of these seem to have lain in the valley which leads
to Foulmire, and the larger part of the surface drainage being probably
directed into this channel, that which is now a tributary seems at first to
have been the most important stream in the district. It ultimately received
the whole drainage from that part of the Chalk escarpment which in earlier
times had contributed its supply to the waters of the older Wardington river ;
the materials of the more ancient deposits being carried down and re-arranged
in the newer valley, forming the gravels, of which remnants still remain near
Foulmire, Foxton, and Harston.

The further extension, however^ of this Wardington stream was limited by
the line of the Upper Chalk escarpment, the recession of which was, and
still is, carried on only at a very slow rate. In the meantime the recession
of the strong spring thrown out by the Totternhoe Stone had given rise to the
commencement of the tributary valley, along which the Rhee now flows, and
this rapidly became an important affluent, cutting off the drainage from the
clay-capped hills on the north and receiving the waters of the springs which
came into existence on the south. The stream at length cut down to the
Gault, and then two fresh elements were introduced among the forces which
were shaping this new valley : the access of water thrown out from the nodule-
bed at the base of the Chalk, and the character of the underlying clay which
yields to fluviatile erosion more rapidly than the Chalk.

Eventually, therefore, a long and wide valley was excavated, which continued
to increase in length and width long after the Wardington stream had ceased
to be an important branch, for we have seen that the southward extension of
the latter was stopped by the Chalk scarp, but the westward extension of the
Rhee Valley progressed till the sources of the springs were cut back to their
present position near Ashwell, with only a narrow watershed between them and
the sources of the river Ivel.

All this could not have taken place until the Boulder Clay had been com-
pletely removed from the district by an earlier system of drainage ; moreover,
the absence of gravel throughout this portion of the Rhee. Valley, from Ashwell
to Barrington, is proof of its recent and rapid excavation, for we should expect
the removal of Boulder Clay to have resulted in the production of extensive
beds of gravel. We conclude, therefore, that this part of the valley, though
now occupied by a river which rivals that in the Chesterford Valley, and drains
an area of about 40 square miles, dates in its commencement from a newer
period than that in which the Barnwell gravels were deposited (see ante,
p. 94.)

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126 GEOLOGY OP THE NEIGHBOURHOOD OP OAMBBIDGE.

CHAPTER XIL-ECONOMICS.

This district, in common with the whole of East Anglia, is very
bare of mineral or other geological wealth, whilst the counties to
the north and west' abound in iron and building stones. We find
in Cambridgeshire scarcely any valuable mineral productions but
the coprolites. The country has a purely agricultural character,
relieved to a small extent only in tne lower-lying parts by lands
under grass for dairy and grazing purposes.

The Oxford and Kimeridge Clays, in the north-western comer, are used,
but not to a great extent, for brickmaking, the largest manufactory being in
the former, near the town of St. Ives.

The Lower Greensand, which elsewhere affords ironstone and phosphate in
small but workable quantities, here consists mainly of sand and loam, but has
not been worked for many years so far as we are aware, even for brickmaking.

The Gault yields a fairly good brick clay, which has been, and still is, exten-
sively used around Cambridge for drain pipes and tiles, as well as for bricks;
the latter are hard and durable, being much better in quality than in
appearance.

The l3ase of the Chalk Marl consists, as has been shown, p. 27 ^
of the well-known '* Cambridge coprohte bed/' which for several
years has been worked to a considerable depth throughout the area
where it occurs, affording employment to large numbers of work-
men.

The first *' diggings " are said to have been about the Eversdens,
and in the neighbourhood of Homingsey, the bed at first being
worked back from its outcrop to a depth of a few feet only.
The cuttings were afterwards reopened and carried back to about
16 feet deep, beyond which depth they could not then be worked
at a profit. But at the present time, from a cheaper method of
working, from the greater value of the phosphate, or from both
causes combined, it answers to extract the bed even 24 or 25 feet
beneath the surface. Attempts have been made to get out the
mineral without removal of the overlying marl, by driving tunnels
along the bed, in fact by the methods similar to those adopted in
mining; but the base of the marl follows the general rule of
dipping in under the higher ground, so that the water within it,
held up by the Crault beneath, has hitherto presented an insuper-
able difficulty to this plan, but we are inclined to think that by
collecting and working out a sufficient number of data, spots might
be found where tunnelling for coprolites could be carried on at a
cheaper rate than 25 feet of overlying earth can be removed.

The method by which the phosphate nodules are obtained con-
sists in digging a vertical trench, with one or more stages, accord-
ing to the thickness of the Chalk Marl which has to be removed.
Many of the pits are 24 to 26 feet deep, and worked in three stages
of 8 or 9 feet each. The vertical face is cut away in great slices by
driving wedges and crowbars into it at a little distance from the
edge, and the material so thrown down being cast out of the trench,

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ECONOMICS. 127

the nodule bed thus exposed is removed to the washing mill, where
the coprolites are separated from their matrix of marl and glau-
eonite.

The mineral-bearing bed is itself of small thickness, perhaps 10
inches may be taken as a fair average, and only one-tenth of this is
phosphate, the bulk consisting of marl and sand. Therefore the
actual deposit of phosphate is equal to a thickness of only an inch
over the area where the bed is known to exist. Supposing the
depth of the diggings to be 16^ feet or 200 inches (which is
below rather than above the average), 200 cubic inches, or 200
cubic yards, of earth have to be removed for every cubic inch or
cubic yard of the mineral obtained.

A cubic yard of phosphate weighs somewhere about two tons, so
that the cost of *^ getting " a ton of the mineral equals the cost of
removing 100 cubic yards of earth. This, with the levelling and
re-soiling of the field, washing the material, cartage, plant, super-
intendence, &c., varies from id. to 5rf. per yard, or from 335. to 40s.
a ton for the phosphate obtained.

The royalty is usually paid not as so much per ton, but at prices
per acre, varying from 100/. to 150?., frequently more than double
the value of the land, as such, excluding the minerals. A bed of
coprolite, equal to an inch in thickness over an acre of ground,
would yield 134 cubic jrards, or say, 270 tons of phosphate. If the
present average price paid per acre for the right of " fossil-digging "
may be taken as 135Z., the royalty amounts to lOs. a ton.

The field to be worked is given over to the contractor for a
stated time, within which he extracts the coprolites, fills in and
levels the pits, restores the top soil, and leaves the surface of the
field very much as it was before ; and its fertility is generally im-
proved rather than deteriorated by the process.

At the top of the Chalk Marl comes the Totternhoe Stone, inVhich are some
large quarries, still open, but which were worked much more extensively in
former times. The stone was much used for building, especially in churches,
and it is still employed for the same purpose to some extent, but not in im-
portant structures (see p. 43).

In the Chalk generally are many pits where the rock is excavated and
burnt for lime, some of the beds being much better suited to the purpose than
others just above or below them. At Linton there is a pit where certain
suitable beds of chalk are quarried and tunnelled for the manufacture of
whiting.

llie flints from the Chalk are used for road-making and mending, also for
building walls and houses, all external angles being built in brick or stone.
For inferior buildings the flints, with other pebbles, are used just as found,
thus producing an uneven face to the wall ; but for churches and important
buildmgs some are split through the centre and built in so that the black and
nearly flat fractured surface shows on the exterior. Sometimes devices are
sunk in buttresses or other stone work, and neatly filled in with dressed black
flint ; some fine specimens of this kind of work are found in Cambridge-
shire.

AgricuUiire.

Speaking of the chalk land east of Swaffham Bulbeck the Rev. L. Jenyns
says* : — "These lands are very good for wheat, and that especially grown on
the chalk hills in the vicinity of BurweU is generally more forward than in
other places, and the earliest in the market. Much corn is likewise now
grown in the reclaimed portions of the fen, but it is liable to be mildewed

* Observations in Meteorology, pp. 367, &c., 1858.

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128 GEOLOGY OF THE NBIGHBOUBHOOD OF GAMBHID6E,

in wet seasons and is always comparativelir late. Hic time for cutting wheat
at Swaffham Bulbeck, on an average of 12 years, I have found to be the
doth of July ; but in some hot and dry seasons it has commenced as early
as the 16th/'

As regards climate, he sa^s : — " Cambridgeshire must have improved in this
respect. The extent to which drainage has been carried on in modern times
can hardly have failed to render the climate less humid. Thousands of
acres which were formerly more or less under water, at least during the
winter, have been reclaimed in this way and brought into cultivation ; the
fertility of the soil being greatly improved by a top dressing of clay (Gault),
dug up from underneath the moor. Crops of oats are usually first sown,
and these after a time are succeeded by wheat."

The Boulder Clay as a rule, but not invariably, supplies an excellent dress-
ing for many kinds of land, a fact discovered and turned to account long ago,
if the many old pits in it may be accepted as evidence. As it is made up of
the detritus of many and various rocks, and usually contains much chalk, it
rapidly disintegrates by exposure to the weather, and it can scarcely fail to
improve the fertility of the soil over which it may be distributed.

This clay generally makes a good soil, especially for com, and (to those who
know the cause of its productiveness) the repugnance of many farmers to
allowing their ploughs to go down to it is most unaccountable. But they
will not, in many parts even now, allow the " raw earth " to be turned up tf
they can help it ; and yet there could be no more sure means of improving
their land, if done gradually and with discretion. This prejudice is, however,
beginning to give way, and will rapidly disappear before the extension and
the excellent results of steam cultivation. There are some parts in which the
sudden introduction of deep ploughing has been temporarily the reverse of
beneficial ; in some others it perhaps has been permanently so. But in by
far the great majority of instances, especially on Boulder Clay, the deep stirring
of the subsoil, the consequent drainage and exposure of more material to
atmospheric influences, has produced, or will produce, great additional
fertili^.

The deposits which rest on the Boulder Clay at the higher levels, although
not extensive, are useful in some of the districts where they occur ; the loams
being dug for brick-making, the gravels for road-mending. The " ancient
river " gravels are as a rule too full of chalk to be much used for repairing
roads, but the more flinty portions and the large stones are used for that pur-
pose, as, for instance, from the large pit N.W. of Newmarket.

The more recent gravels are very largely dug in the town and neighbour-
hood of Cambridge, near St. Ives, and elsewhere, being used for railway
ballast as well as for road-making.

The soil of the Fenland is highly productive, and is mostly under culti-
vation; the branches of fen up the main valley pass gradually into the
ordinary alluvial soil, which makes excellent pasture. The marshes, or strips
of alluvium, are subject to sudden floods, the water firom the surrounding
high hinds being headed back by want of passage room where they discharge
into the washes of the fens.

Water Supply.

It has been stated that the thickness of the Oxford Clay in this
part is not certainly known, we cannot, therefore, assert to what
depth a boring would have to be made to reach the underlying
more permeable strata. But we are convinced that if once the clay
were pierced, an abundant supply of water, rising nearly or quite
to the surface (according to the site of the boring), would at once
be obtained.

In both the Oxford and Kimeridge Clays are bands of limestone, nodules,
or septaria, along which water sometimes percolates, in most cases very slowly,
but wells have been made in which fair springs from this source have been met
with. There is no certainty of getting water from these bands, as in thewells
at Conington and Bluntisham (pp. 159, 167,) a depth of 300 feet was reached
without success ; but in one at Redhill, a farm west of Conington, a good

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ECONOMICS. 129

spring was met with at a depth of 12 feet. Such a source of supply would, of
course, be available for a limited consumption only.

The Lower Greensand is usually found to be an excellent water-
bearing formation, but its capabilities in this respect are probably
much greater where it Jies beneath the Gault than at its outcrop.

Where the Lower Greensand is reached by boring through the
Gault in this area, an abundant supply of water is invariably
found. Not always directly the latter formation is penetrated,
although there may be sand directly beneath it, but at no great
distance below a "rock" is pierced, from which the water rises
frequently to a height of some feet above the surface of the ground.
Borings at Harston, Whaddon, and Wendy may be mentioned as
instances where iron pumps have been erected over the bore-holes,
the water being constantly discharged through the spouts in un-
varying quantity and temperature.

The coprolite workings are supplied with water by boring into
the Lower Greensand, large quantities being necessary for washing
the matrix away from the " fossils." Indeed, were it not for the
abundant supply obtainable at slight cost by these borings, the
coprolite industry could never have been so profitably developed.

The Gault, like the Jurassic Clays, affords no sprinj? s of its own worth
mention, but its surface, when overlaid by Chalk Marl, holds up the water
that has percolated through the latter, and this constitutes what is locally
called the " fossil spring," from its occurring at or in the bed which encloses
the " coprolites." This is the spring which prevents tunnelling for " coprolites "
being carried on with advantage.

The Chalk here, as elsewhere, is pre-eminently a water-bearing
formation, any wells carried down to the line of saturation being
invariably supplied. In this area, where the Chalk comes to the
surface, the line of saturation is naturally low down on the for-
mation, being quite at its base along the boundary. As the Chalk
dips down the hne rises, not relatively only as the Chalk base falls,
but actually beneath the higher ground. Until the Chalk passes in
under impervious Eocene beds or Boulder Clay, it is necessary for
All wells that depend on a supply from below the line of saturation
to be dug down to it, as the water would not rise in a boring. It
is only when the line of saturation is depressed by an overlying im-
pervious stratum that this result can be obtained.

The line of saturation almost invariably rises beneath high
ground in a Chalk area, because the rain which falls on the surface
percolates downwards, and feeds the sources of supply as quickly
as the water is drawn off by the springs and .streams of the district.
As the water-level falls, and the hydrostatic pressure lessens, the
springs and streams fall off, as it rises tney increase; thus a
general balance is maintained, the height of the line rising above
the spring before it can counteract the friction of the water passing
through the rock. The line, therefore, has a definite and constant
relation to the main and minor valleys of a district, abnormally
affected in some instances by the dip of the beds. A good instance
of this is furnished by the Gog-Magog Hills, where a synclinal dip
depresses the water line by throwing out the splendid springs which
supply the town of Cambridge.

We have been enabled to work this point out in a detailed man-
her through the kindness of Mr. H. Tomlison, C.E., Engineer

N309. T

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130 GEOLOGY OF THE NEIGHBOUBHOOD OF CAMBRIDGE.

to the Cambridge Waterworks Company, who has famished us
with the particulars of many wells in the neighbourhood. From
these we nave constructed two nearly parallel lines of sections.
Figs, 2 and 3, Plate 5, running along the flanks of the Gog-Magog
Hills, and connected them by a cross section (Fig. 1, Plate 5).
Wells have been dug at all the points indicated to a few feet
below the line of saturation, and these show it to be as represented
by the continuous lines a, a, in the diagrams.

It will be seen that the water-level rises generally under the
higher parts of the surface, from N.W. to S.E. along the longi-
tudinal sections; and it has a tendency to rise &om Fulbourn
Mill towards the Hills Farm, as well as from Stapleford Mill to-
wards Heath Farm in the cross section. But a sudden local
depression occurs, the greatest amount of which is beneath the
highest ground of the Gog Magog Hills, where it might be ex-
pected to be relatively high, and to follow the dotted lines 6, ft, in
the sections. The line of greatest depression coincides witfi the
line of hills, and passes from Copley Hill, through Vandlebury,
west of the Quaker's Charity Farm, towards Cherry Hinton.

There is no doubt that the Chalk here lies in a synclinal hollow
or trough, the inwards dip from each side having mainly con-
tributed to the formation of the hill by preserving its beds, while
those on either side were removed by denudation. The broken
lines represent the lines of division of the Lower Chalk, dipping
towards the escarpment in the longitudinal sections and in the
cross section forming synclinal troughs beneath the Gog-Magog
Hills.

It will be seen that there is a great correspondence between the
cross section of the larger of these troughs and that of the line of
saturation, although the latter under normal conditions would
diflfer from the former in being higher rather than lower along the
central line. There is probably some connexion between them, of
which we believe the following to be the true explanation.

The Tottemhoe stone, at the top of the Chalk Marl, holds the
water that has percolated down to it through the overlying per-
meable chalk, as is shown by the line of springs which frequently
follow its outcrop. The stone is here, in common with the other
beds, thrown into a trough, along the bottom of which water would
flow somewhat more freely than elsewhere. We have shown that
the line of depression (which coincides with that of the hills)
extends towards Cherry Hinton, where there is one of the finest
springs in the country. This spring, where the trough runs out
to the surface of the ground, throws out (owing to that circum-
stance) an undue proportion of water, thus permanently lowering
the line of saturation along the synclinal axis where the water
moves most freely.

Water, even permanent springs, may be met with in fissures In
the Chalk before reaching the line of saturation, but it is always
most uncertain; indeed the whole thickness of the Chalk may be
penetrated without finding any great quantity of water. But there
are generally some indications, especially in wells that are dug to
any depth, which, if observed in connexion with the dip, structure,
and general conditions of the beds, may lead to the desired result

The Boulder Clay is sometimes shghtly permeable, and weHs

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ECONOMICS.. 131

sunk in it, which fill slowly with soakage water, are the sole sources
of supply of many villages in the district. The water is generally
very hard, but otherwise not of bad quality.

The Gravels, where resting on clay, are, of course, water-bear
ing, and they supply most of the towns and villages situated upon
or near them. The water they yield would be excellent but for
the risks, almost certainties, of pollution by drainage. We have
tested many samples of such waters and always found them more
or less contaminated.

It is easy to understand that wells would be sunk in such deposits
wherever a supply of water was required, or near each house in
the towns and villages. But one fails to see why much should
have been made of springs, where, through some local condition
of the beds, water that has percolated through the gravel and sand
of a graveyard is thrown out ! Three sucii cases occur within
our area, one at Hadstock, where the spring is enclosed by brick
walls, and the water is highly esteemed by the villagers. It may
be, however, that the difficulty of drawing and fetching water from
the deep wells at the neighbouring farms has some influence on
the meed of praise bestowed upon that from the spring.

Another instance is at Somersham, where a brick arch, with an
iron gate, has been in former times erected over a spring within
the precincts of the old Bishop's palace. The palace has been
razed, but the spring, with its protecting arch has been preserved.
Yet it is inevitable that some at least of the water must have
percolated through the gravel on which the adjoining graveyard
stands.

In an analogous case an arch has been erected over a spring,
and an inscribed brass-plate built in, to hand down to posterity
the name of the benefactor I The water here is thrown out at the
junction of Oxford Clay with gravel, in a low comer of the church-
yard at Holywell, and is therefore subject to peculiar risk of con-
tamination.

This spring in the churchyard, or " Holy Well," as it was doubt-
less called, must have given its name to the village ; and we find
many other instances in this area in which the names are due to
some physical peculiarity. There are Fenny Stanton and Long
Stanton, both villages or " towns " on deposits of gravel or "stone,''
Fenny Drayton (Dry-town) and Dry Drayton, Fen Ditton and
Wood Ditton, or Ditch-end, one being at each termination of the
^'Devil's Ditch."

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132 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

APPENDIX A.

PALAEONTOLOGY.

By R. Etheridgb, F.R.S., L. and E., F.G.S.

L General Account op the Paleontology op the Dippebent

Sub-Divisions op the Chalk.
In preparing the lists of Fossils and Appendix to this Memoir much attention
has been bestowed upon the naming and distribution of the species obtained
by our collector, Mr. H. Allen, in the area under description. No less than 43
localities have been searched, collected from, and recorded in the text under
the following divisions, horizons, or zones : —
I'l. The Cambridge Greensand.

I 1. ine v^amDnage ureensana.
Lower < ^' " Chalk Marl, from 7 localities.
I 3. „ Totternhoe Stone, from 6 loca

Totternhoe Stone, from 6 localities.

14. „ Zone of Holaster subglobosus, from 5 localities.

r5, „ Melboum Rock, from 6 localities.

Middles ^' '* Zone of Rhynchonella Cuvieri, from 6 localities.

I 7. 9, „ TerebratuUna gracilis, from 6 localities.

LS. „ Chalk Rock, from 4 localities.

Upper 9. „ Zone of Micraster cor-bovis, from 6 localities.

1. Cambridge Greensand.
The Geological Survey has not collected largely from the Cambridge Green-
sand, that being quite unnecessary in the face of such materials gathered
together and named in the Woodwardian Museum.

The list of fossils given on p. 30, and numbering 65 species, has been com-
piled by Mr. Jukes-Browne from sources other than those of the Geological
Survey. No less than 47 species of Invertebrata have been obtained from the
matrix of the Coprolite or Phosphatic nodule beds in the neighbourhood of
Cambridge. The fossils generally referred to the Cambridge Greensand are far
more numerous, but most of these are believed bv Mr. Jukes-Browne to
have been derived from the Gault. An analysis of the whole fauna will be
found in Mr. Jukes-Browne's paper upon "The Relations of the Cam-
bridge Gault and Greensand,''* in which he discusses the age of the so-called
Cambridge Greensand, and compares its fauna with the Vraconian of Prof.
Renevier, and also with that of the Gault of Folkstone and Bucking-
hamshire.

There can be no doubt about the close relationship between the fauna of
the Cambridge Greensand (excluding the derived fossils), and that of the
Chalk Marl; the two doubtless form one palseontological zone, about 50 per
cent, of the Invertebrata being common to both. The following species and
varieties have been founded on specimens obtained from the Cambridge Green-
sand, and have not been met with elsewhere. Some of these may therefore
be considered as characteristic of this bed.

Anomia transversa, Seeley. Rhynchonella lineolata, Phill.

Lima omata, Ether. Cidaris gradata, Seeley.

Ostrea cunabula, Seeley. „ Sedgwickii, Seeley.

„ lagena, Seeley. Echinocyphus impressus, Seeley.

Plicatula minuta, Seeley. Goniophorus lunatus, Ag. var. Mi-

Onchotrochus Carteri, Duncan. nutus, Seeley.

Pharetrospongia Strahani, Sollas. Salenia Woodwardii, Seeley.
TerebratuUna striata, var. triangularis. Ether, is also characteristic from its
abundance at this horizon, though it also occurs in the overlying marl. It is
remarkable that Rhynchonella lineolata has not been obtained from any other
bed in the Upper Cretaceous Series except this and the Red Rock of Hun-
stanton, where one or two specimens have been found.

R, Martini has not yet been detected in the Cambridge Greensand.

* Quart. Joum, Geol. Soc, vol. xxxi. pp. 256-316 (1875). Supplementary
Notes in vol. xxxiii. p. 485 (1877).

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PALiEONTOLOGY. 133

I must, however, notice the series of fossils collected by us from the 8 other
horizons or zones, and from 44 localities.

2. Chalk Marl.

The seven following^ localities were collected from : Kingston, Harlton,
Hauxton Mill, Madingley, SwafPham, Reach, Burwell (Victoria Quarry),

From these 7 quarries 21 species were obtained, the individuals of most
heing abundant, the number of Lamellibranchiata and Brachiopoda however
predominating; in the former groups 5 species were collected, in the latter 8.
Only one Cephalopod {Ammonites varians) has been found. An analysis
of the 21 species gives their distribution through the 7 areas as follows : —
Kingston, 8 species; Harlton, 12; Madingley, 11 ; Hauxton, 8; Swaffham, 6;
Rea<;h, 11; Burwell, 9.

Two species of Fish ; 1 Cephalopod ; 5 Lamellibranchiata ; 9 Brachiopoda ; 3
Echinodermata ; and 2 Annelida. The two chief groups, the Lamellibranchiata
and Brachiopoda, are equally distributed through all the quarries, Plicatula
inflata and Terebratula semiglohosa occur in all the localities. The table
at page 42 shows the distribution of the 22 species. Rhynchonella Martini is
common in the Chalk Marl, and seems to take the place of R. lineolata of the
Cambridge Greensand.

3. Tottemhoe Stone,
From this zone, which is better defined physically than palaBontologically, the
Survey has collected 43 species ; in addition to these I have added a supple-
mentary list of 42 species from the Woodwardian Collection, chiefly from the
famous quarries of Burwell ; these include the 12 new species and varieties,
also from the Woodwardian Collection, described by myself in this Appendix.

The six localities searched and collected from in this Zone are : — Harlton,
Haslingfield, Orwell, Cherry Hinton, Fulbourn Cutting, and Burwell.

Thirty-eight of the 43 species occur at Burwell, every form being in the
Woodwardian Museum. The only species in the list named not represented
at Burwell are Cidaris dissimilis, Onchotrochus serpentinus, Holaster subglobosus,
and forms of Beryx, and Lamna. The Fauna known to us from this Zone
embraces the following : — Fish, 7 species; Cephalopoda, 17; Gasteropoda, 8;
Lamellibranchiata, 26 ; Brachiopoda, 9 ; Echinodermata, 7 ; Crustacea, 5 ;
Annelida, 3 ; Actinozoa, 3 ; or a total of 86 species.

To the Fauna collected at Cherry Hinton and Burwell I have added 7
new species and 5 varieties, but these were in the Woodwardian Collection,
and we were allowed by Prof. Hughes to select, describe, and figure them fo
the present Memoir. They are the following : —
Scalariafasciata, Ether.

Anomia papyracea, D'Orb., var. Burwellensis, Ether.
Amculafilata, Ether.
„ dubia. Ether.
Inoceramus conveoms. Ether.

„ „ var. quadratus, Ether.

„ latus, Mant., var. Reachensis, Ether.
Lima echinata. Ether.

Ostrea curvirostris, Nilss., var. injlexa, Ether.
Pectenjissicosta, Ether.

Terehratulina gracilis, Schloth., var. nodulosa. Ether.
Pinna tegulata. Ether,
all these, with others, are described further on.

The species collected by the Geological Survey were distributed through
the localities as follows : — Harlton and Haslingfield, 15 species ; Orwell, 14 ;
Cherry Hinton, 15; Fulbourn Cutting, 11 ; Burwell, 38.

The supplementary list of 42 species from Burwell obtained from the Wood-
wardian Collection embraces an important series of forms, and shows the wealth
of species contained in the Tottemhoe Stone from this one locality; those
collected by us from Burwell bring up the number to 85 species.

A comparison of the list of fossils on p. 49, with that of the Zone of Holaster
subglobosus shows that comparatively few species are confined to the Tottem-
hoe Stone, and that the greater number of those which are most abundant
individually, rangfe into the overlying beds; this renders it a matter of
doubt, as to whether the Tottemhoe Stone can be regarded as a separate

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134 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBEIDGE.

divifiiion or zone on strictly palaebntological grounds ; there are, however, many
species that appear to be confined to the Totternhoe Stone.

The Cephalopoda are a distinctive feature in the Totternhoe Stone, many
making their first appearance in this grey sandy chalk. The constant presence
and abundance also of certain Brachiopoda {Rhynchonella Mantelliana, R,
grasiana, Kingena lima) is significant, vlsoPecten orbicularis, although these are
not absobitely confined to it. It is Burwell that yields the rich fauna of the
zone. The Woodwardian Collection contains nearly every form. The Totternhoe
species quadruple in number those in the preceding Chalk Marl, as well as
possessing a distinctive facies in the groups, many new forms appear. Pinna
tegulata, Pecten Jissicosta, Lima echinata, &c., and varieties of Terebratulina,
A comparison of the Burwell species with those found in bed 5 of the Folk-
stone section given by Mr. F. G. H. Pbice,* exhibits great resemblance. The
sudden appearance of so many forms in the succeeding zone clearly show
a great change of life over the same area at the time of deposition ; it is also
worthy of notice that Holaster svbglohosus has not been found at Burwell or
Cherry Hinton, only in the basement nodule bed at Shepreth. The nodular
variety of TerebratiUa gracilis is almost confined to this horizon, as well as a
large torm of Micrabacia coronula, those in the Cambridge Greensand being a
different variety of this coral.

4. Zone of Holaster subglobosus.

This palaeontological horizon is here used in a more restricted sense than
by Dr. Barrois (see table, p. 21). We have collected from the following five
localities in it: — Shelf ord Clunch Pit, Shelf ord Limekiln, Cherry Hinton,
Eversden, and Pit N.N.E. of Orwell.

From these quarries 40 species have been determined from a large series
collected by Mr. Allen, 'fhe following numbers show how unequal is the
distribution of life through certain parts of the Chalk ; but as most of the
species are rather of a deep sea character, we should expect both prolific and
barren areas.

The Shelford Clunch Pit yielded 11 species; Limekiln, 23 ; Cherry Hinton,
26; Eversden, 11; the Pit N.N.E. of Orwell, 14, Holaster subglobosus
occurred plentifully at the first three localities, but was not found in the
other pits which were richer in Brachiopoda ; these numbers would probably
be greatly increased bv more prolonged collecting.

No Fish were found in the. last two localities, and the Cephalopoda are chiefly
confined to the Orwell Quarry.

The 40 species fall under the following groups : — Fish, 6 species ; Cephalo-
poda, 4; Lamellibranchiata, 13; Brachiopoda, 7; Echinodermata, 7; Anne-
lida, 1 ; Crustacea, 2.

The species of Holaster giving it& name to this zone has a very important
bearing upon the distribution of a definite and well determined form over a
very large area. Its vertical range in the southern part of England and the
northern part of France, according to Prof. Hubert, is cOnsiderable,.including
the whole of the Chalk Marl and Grey Chalk of England. Whether we can
separate this zone in England into the four subdivisions as proposed by
Barrois, is questionable. It is true we have two species of Ammonites {A. Rho-
tomagensis and A. varians, occurring here with the Urchin; A, varians also
occurs in the Chalk Marl at Reach and in the Totternhoe Stone at Burwell,
but we have not found it above the zone of Holaster subglobosus ; a far more
complete search must be made for species through these lower divisions of the
Chalk before we can correlate even the Cambridge, Bedfordshire, and Hertford-
shire sub-divisions with those of the London Basin, much more with those of
the north of France ; but Hubert and Barrois, by their researches over the
last area, have done more to clear up the distribution of life through the Chalk
than any other Palaeontologists.

5. The Melbourn Rock.

Only 15 species have been collected from this horizon, and from the follow-
ing localities : — Litlington, 7 species ; Royston, 6 ; Melbourn, 25 ; Harston, 9 ;
Shelford and Cherry Hinton, 7 ; Swaffham Bulbeck, 4.

These 15 species are thus distributed : — Fish, 5; Cephalopoda, 2; Lameli-
branchiata, 4 ; Brachiopoda, 4. No Echinodermata, Annelida, Crustacea, or

* Quart, Journ. Geol. Sac, vol. xxxiii., p. 431.

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PAL^ONTOLOGT. 135

Aetinozoa seem to occur in the Melbourn Rocfc^ and^ looking at the paucity of
species as well as groups^ we may believe that the sediment was not favourable
to the conservation of animal remains. Rhynckonella plicatilis and a variety
of Ostrea vesicularis occur in every quarry. The Fish remains were only in
the form of teeth, vertebrae, and coprolites ; the typical form of Belemnitella
plena occurs at Royston, Melbourn, Harston, Shelford, and Cherry Hinton.

6. Z(me of Rhynckonella Cuvieru

This division of the Middle Chalk (with few flints) corresponds to the zone
of Inoceramus labiatus, of Barrois.

The species of Rhynckonella, giving its name to the zone, from its small
vertical distribution, is very abundant at every locality except Wilbraham,
where it has not been observed ; a more diligent search in the railway cutting
would doubtless discover it there also.

This zone is poor in species, if we may judge from the collection made
from the five localities, only 14 being procured by Mr. Allen, viz. : — Fish,
1 species ; Lamellibranchiata, 3 ; Bracniopoda, 6 ; Echinodermata, 3 ; Anne-
lida, 1. From Stanmoor Hall pit, 3 species were obtained ; from Babraham, 10 •
Little Trees Hill, 4; railway cutting near Wilbraham, 3; and Mistleton
Hill, 9.

The Brachiopoda greatly predominate in this horizon, especially at Babra-
ham, where all the six species occur, the characteristic shell Rhynckonella
Cuvieri being also present in four out of the ^ve localities, and Terehratula semi-
glohosa in three of the ^vt. It is evident that we are but imperfectly acquainted
with the' fauna of this and the preceding division, but small as is the number
of species known in these horizons, still two new forms of Echinoidea occur,
Eckinoconus ghhosus and E. subrotundus, and with these Inoceramus myiiloidesy
Rhynckonella Cnvieri, and Terebratulina gracilis have reached their maximum
development.

Mr. Jukes-Browne, in a note to me descriptive of this horizon, remarks
that Prof. HiBBERT long ago indicated the abundance of Inoceramus laUatus
in the Turonian of D'Orbigny, and that Pr. Barrois employed its name to
designate the lower part of this division, proposing at the same time to
consider the upper beds as the zone of Terebratulina gracilis. He also states
that "certain forms of this little Brachiopod are very abundant in, and
perhaps confined to, this portion of the Middle Chalk, but occur also in
the lower zone, and Inoceramus labiatus is equally common in both;" he
believes, therefore, that the two zones will ultimately be distinguished by
different species of ammonites, as already pointed out by Dr. Barrois.

Fragments of another Inoceramus seems also to be abundant here ; this I
have figured as the /. problematicus of D*Orbigny (Plate 3, Fig. 10-11).

7. Zone of Terebratulina gracilis.

This division of the Lower Chalk is immediately below the Chalk Rock,
is about 150 feet thick, and agrees in position to that assigned to it by Barrois
in France and this Country; the species T. gracilis which gives name to the
beds, and also T. striata occur only in the lower division of the zone, and were
collected from the three localities in the lower beds, whilst those in the
upper beds have not produced any. The result of our collecting has been
25 species, from 7 localities : Worsted Lodge, Mutlow Hill, and Missleton
Hill (all in the lower beds) ; Linton, Westley Waterless, and a pit near Dul-
lingham Station (all in the upper beds) ; 8 of the 25 species are confined to
the lower division, 12 to the upper, and 5 are common to both. The fauna!
distribution through the quarries in the lower and upper divisions is as
follows: — ^Worsted Lodge, 10 species; Mutlow Hill, 8; Missleton Hill, 9;
Linton, 8; Westley Waterless, 11; pit near Dullingham Station, 6; and
Carleton Grange, 5.

The Echinodermata and Brachiopoda appear to have abounded in this region,
6 genera and 8 species of the former being collected by Mr. Allen, together
mth 7 species of Brachiopoda, 7 species of Lamellibranchiata (all monomyarian),
1 Coral, and 1 Protozoa complete the number. The individuals of the above
three chief groups were abundant, the Ventriculitidae and Protozoa generally are
very sparingly distributed through the Chalk of Cambridgeshire, one genus
only {Ventriculites) being determined in all coUections made, and only one

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136 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

species ( V. mammilaris) occurs in this zone. Terebratulina gracilis var. lata is
the T. gracilis occurring in and determining this horizon ; the species T. striata
being much more sparingly distributed; Cidaris septrifera, Cyphosoma
radiata, Holaster planus, and Mipraster cor-bovis occur only in the upper
beds of the zone, while Echinoconus suhrotundus is confined, as far as we
know, to the lower division.

8. Zme of the Chalk Rock, .

This thin but well defined bed is characterised in this area by the abundance
of Holaster {Spatangus) planus, which also determines this horizon in Buck-
inghamshire, Hertfordshire, Berkshire, &c. It is a constant zone throughout
the greater portion of the northern part of the London Basin, dividing the
Middle from the Upper Chalk, or occurring at the top of the Middle Chalk
as now recognised (formerly called the Lower Chalk). It is also characterised
by the presence of several Gasteropoda, but they chiefly occur in tbe form of
casts.

We have collected from six different localities on this horizon ; individual
specimens are tolerably abundant, but only 24 species have rewarded the search
in this area. The localities examined are as follows : — Reed and Barkaway
(yielding 17 species, including the new form Rhynchonella Reedensis) ; Great
Chesterford (yielding 8 species); Carleton Grange (4 species); Westley
Waterless, No. 1 (10 species); Westley Waterless, No. 2 (15 species); and
Stetchworth (8 species).

Terebratula semiglohosa and Ter. camea appear to occur at all the localities,
the Micrasfers at most of them, Ananchytes ovatus at three, and the charac-
teristic Holaster planus at four. Only two species of Cephalopoda appear
amongst the series collected. Ammonites Prosperianus and Scaphites cequalis, see
table of distribution, p. 128, and the former of these is as characteristic of the
rock as the above-mentioned echinoderm.

The fauna of the Chalk Rock is somewhat peculiar, doubtless physical con-
ditions greatly influenced the development and distribution of life. A few
species seem to be almost confined to this division ; two of these, however
(Rhynchonella Reedensis and Holaster planus), occur also in the upper part of
the underlying zone, but have not been found above it in this area, notwith-
standing the careful search made by Mr. Allen. The new form of Rhyn-
chonella (R, Reedensis) may be only a variety of either JR. Cuvieri or of R.
plicatilis, its variation being due to the circumstances under which it lived, but
no such variety makes its appearance in any lower beds, and well marked
R. plicatilis occur with it in the Chalk Rock.

9, Zone ofMicraster cor-bovis.

This zone forms the base of the white Chalk with Flints or true Upper
Chalk, and is equivalent to the lower portion of the Senonian of D'Orbigny,
with its characteristic Micraster cor-testudinarum ; at present we have not
detected the typical form of this species in our Upper Chalk, Micraster
cor-bovis or some variety of M. cor-testudinarum being its representative.
Dr. Barrois gives as characteristic and typical localities for M, cor-testudi-
%arum Cuckmere Haven, in Sussex, Stockbridge, Winchester, and Pangbourn.
The small difference between this species, as figured by Goldfuss, and M.
Vor-bovis, or even varietal forms of M. cor-anguinum may mislead us; its
recognition, therefore, as a typical zonal form in this area must be deferred
until the characteristic species has been found and well determined.*

We have collected from the following localities in this division of the Upper
Chalk : — Chesterford and Saffron Walden (9 species) ; Balsham Limekiln
(9 species) ; Balsham,»N.N.E. of (9 species) ; Stitchworth (6 species) ; Westley
Waterless (4 species) ; together they have yielded 18 species illustrating the
following groups : — Lamellibranchiata, 3 species ; Brachiopoda, 4 species ;
Echinodermata, 7 species; Polyzoa, 2 species; Protozoa, I species; Actinozoa,
1 species.

The individuals were numerous, Micraster cor-testudinarum ? (var.) occurred
in all the localities, M. cor-bovis and M, cor-anguinun in four. Balsham also yields

* Since writing the above Dr. Barrois has forwarded to me a specimen of M. cor-
testudinarum obtained by him at Cuckmere Haven, Sussex.

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PAL^ONTOLOGT.

137

3 of the 4 Brachiopoda, 3 of which are confined to that locality. No other
group but the Echinodermata occurs at Westley Waterless, the 3 species above-
named, which are also common to all localities, and Cyphosoma radiatumy
which is also found at Balsham.

With regard to the grouping of these zones into larger divisions, and the
grounds for estiablishing a Middle Chalk, Mr. Jukes-Browne has sent me
the following observations :— ^

The PalcBontological Relations of the Lower and Middle Chalk.

In this Memoir we have proposed a triple division of the Chalk, and have
shown that in -what has hitherto been called the Lower Chalk there exists a
band of rock possessing peculiar lithological characters, and forming an horizon
as marked and distinct as that of the Chalk Rock above. This band we have
identified with the bed of marl containing Belemnites pUnus, which has been
found in so many sections in the south of England, and has been described
by Dr. Barrois* and Mr. F.. G. H. PRiCB.t

The beds of Chalk above and below the horizon differ somewhat in their
lithological characters, but still more markedly in their fossil contents ; an
examination of the two faunas has indeed revealed such great differences that
the change in the forms of life assumes the importance of a palseontological
break in the series. The desirability of the classification proposed is thus
strikinglv'confirmed.

Out or the 90 named species of InvertebrataJ which have been obtained
from the Lower Chalk of Cambridgeshire (as now defined), only eight have
actually been found in the beds above the Melbourn Rock ; seven more are
known to have a wider range, but no less than 74 have apparently died out
during the interval between the deposition of the Lower and the Middle
Chalk ; the following is a hst of these forms : —

Cephalopoda.

Ammonites cenomanensis, D'Arch,

„ Lewisiensis, Mant.

„ Mantelli, Sby,

„ navicularis, Mant.

„ rhotomagensis, Defr,

„ varians, Sby,

„ „ var Coupei, Brong.

Belemnites plenus, Blainv,

Gasteropoda.

Cerithium ornatissimun, Desh, | Scalaria fasciata. Ether,

Dentalium majus, Gardner. \ Solarium dentatum, Desh.

Lam ELLIBRANCHIATA.

Nautilus DeslongchampsianuSjD' Orb.

„ elegans, Sby,

,, pseudoelegans, lyOrb.
Turrilites costatus. Lam,

„ Scheuchzerianus, Bosc.

„ tuberculatus, Bosc.
Scaphites sequalis ? Sby.

Anomia papyracea, UOrb.
Avicula filata. Ether.
„ dubia. Ether,
„ gryphaeoides, Sby,
Exogyra haliotoidea, Sby.
Inoceramus convexus. Ether.

„ „ var. quadrata, Ether.

„ latus, var. Reachensis,

Ether,
„ striatus, Mant,

Lima aspera, Mant,
„ echinata. Ether.
„ globosa, Sby.

Ostrea acutirostris, Nilss,

„ curvirostris, Nilss,

„ &ons, Park.

„ Rauliniana, D*Orb.
Pecten elongatus. Lam.

„ fissicosta. Ether,

„ orbicularis, Sby.
Pholadomya decussata, Sby.
Pinna tegulata, Eth.
Plicatula inflata, Sby.
Radiolites Moretoni, Mant,
Spondylus aequicostatus. Ether.

* Recherches sur lo Terrains Cretac^s Sup^rieurs, ZiV/e, 1876.
f Quart. Journ. GeoL Sac., vol. xxxiii.., p. 431.

J The species peculiar to the Cambridge Greensand and named on p. 132, are
not reckoned in this number.

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138 GEOLOGY OF THE NEIGHBOURHOOD OF OAMBBIDGIB^

Braghiopoda.

Argiope megatrema, Shy.
Kingena lima, Defr,
Rhynchonella ffrasiana, D'Orb.

* „ Mantelliana, Sby,

* „ Martini, Mant^
Terebratula biplicata, Sby,

Terebratula squammosa, Sby,
„ sulcifera, Morris.

Terebratulina gracilis, yar. nodulbsa,
Ether.
I, striata^ yar. triangularis.

Annulosa.

Glyphsea cretacea, M'Coy.
Necrocarcinus Woodwardi, Bell.
Enoploclytia brevimani, M*€oy.

„ Imagei, Mant,
Pallcega Carteri, Woodw.

Pollicipes arcuatum, Darwin,

„ unguis, Sby.
Serpula annulata, Sby,

,, rustica, Sby,

Yermicularia umbonata, Mant.

Echinodermata.

Cidaris Bowerbankii, Forbes,
„ Dixoni, Cotteau,
„ vesiculosa, Goldf.

Discoidea cylindrica. Lam.
„ subucula, Klein.

Hemiaster Morrisii, Forbes.
Holaster laevis, var. trecensis, Leym.

„ subglobosus, Leske.
Pseudodiadema.
Pentacrinus Fittoni, Ansten.

ACTINOZOA.

Micrabacia coronula, Goldf, \ Onchotrochus serpentinus, Duncan.

It may be objected that the Middle Chalk of Cambridgeshire has not been
searched so completely as the lower beds, and consequently that the requisite
data for such a comparison have not yet been obtained. This is to some
extent true, and only 30 species have hitherto been found in this division ;
yet there can be little doubt that it does not possess so large and varied a
fauna as that of the Lower Chalk ; moreover, we are fortunately able to point
to other areas which have been still more thoroughly examined, the result in
every case being to reveal a striking contrast between these two faunas.

Thus, in his description of the chalk between Folkestone and Dover,t Mr. F.
G. H. Price has catalogued 96 Invertebrates from the Chalk Marl and Grey
Chalk; only three of these range upwards into the overlying beds, viz.. Go-
master mosaiciis, and the ubiquitous forms Ostrea vesicularis and Terebratula
semiglobosa. From the two zones forming the Middle Chalk he records 1 9 species,
including the three above mentioned ; thus though some additions will pro-
bably be made to the latter fauna, it is clear that here also the two assemblages
are very different, and that the break is marked by the extinction or migration
of a very large number of species.

In the Isle of Wight Dr. Barrois mentions 41 species as occurring in the
Chalk Marl and Grey Chalk, and 18 species in the two zones of the Middle
Chalk ; only three being common to both divisions. In Sussex, he quotes 24
species from the Cenomanian and 23 from the Turonian (near Lewes) and
there is not one species common to the two lists.

Again, Mr. Caleb EvansJ records 20 species from the Grey Chalk of
Sussex, and 30 species from those beds which appear to represent our Middle
Chalk, and only three species range from one group to the other.

Finally, Dr. Barrois' researches in the north of France enable us to make
a thoroughly reliable comparison between tlie faunas of the Cenomanian and
the Turonian, because large collections have been made from each division.
From the Lower Chalk (zones of Holaster subylobosus trnd Belemnites plenus) he

* These occur doubtfully in the zone above (of Rhynch. Cuviert)»
f Quart. Journ. Gcol. Soc, vol. xxxiii., p. 431.

t On some Sections of Chalk between Croydon and Oxstead. Paper printed by
Geol, Assoc, 1870.

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PALM>]SrTOLOGT.

139

lias in his various papers catalogued a total of 102 Invertebrates; in his recent
memoir " Sur le Terrain Cretac^ des Ardennes "* he gives a list of fossils
from the Turonian of Itie eastern part of the Paris Basin, which numbers 83
species exclusive of the Fish. Only. 15 species are common to the two faunas,
so that the interval beweeu the two periods seems to have witnessed the ex-
tinction of 87 species and the introduction of no less than 68 new forms. We
m&y at any rate assume this calculation to be an approximination to the truth.

This sudden and complete change of life can hardly be attributed to any
sudden or local alteration in the physical conditions, for there is very little
difPerence in the character of the sediment constituting the beds above and
below the Melboum Rock.

We are, therefore, forced to conclude that there is here a break in the con-
tinuity of the Chalk, marking a long lapse of unrepresented time, during
which the conditions of existence throughout the whole province underwent
very considerable but gradual alteration, producing a corresponding effect upon
the life of the province.

It is even possible, as Dr. Barrois has suggested, that in Cambridgeshire
a certain amount of erosion and destruction of previously formed deposits
"went on during this interval. He remaxks upon the diminution in the thick-
ness of the zone of Belemnites plenus in this area compared with its develop-
ment in the south of England and north of France, and considers that *' these
uppermost Cenomanian beds were more or less denuded at the invasion of the
Turonian sea, and that the Belemnites which they contained are now found
rolled and remani^s at the base of the Turonian." ITie structure of the Mel-
bourn Rock and the rolled lumps of chalk which it so frequently cohtains
are decidedly confirmatory of this supposition.

The Middle Chalk of Cambridgeshire appears, therefore, to be marked off by
lines of erosion, one at the base of the Melbourn Rock and the other at the
top of the Chalk Rock, so that these two layers must be included within the
division. That the formation so constituted possesses a fauna that is essentially
peculiar to it has already been established, but we desire to draw special
attention to two classes of animals which are represented by such different
species in the Lower and Middle Chalk respectively that they are of themselves
sufficient to distinguish the two faunas. These two groups are the Cepha-
lopoda and the Echinodermata ; of Ammonites alone the Lower Chalk con-
tains a large number of species, but not one of them has yet been found in
the Turonian or Middle Chalk, which likewise possesses its own peculiar assem-
blage. The following is a list of the commoner species in each of these
assemblages : —

Ammonites of the
Lower Chalk.
Ammonites rhoiomagensis, D' Orb,
cenomanensis, D'Orb,
navicularis, Mant,
Mantelli, Sby,
Lewisiensis, Mant,
varians, Sby,
falcatus, Mant,

Ammonites of the

Middle Chalk.
Ammonites nodosoides, Schl.
„ rusticus, Sby,
„ Woolgari, Mant,
„ carolinus, D'Orb,
„ peramplus, Sby,
„ var. Prosperianus, D'Orb .

The Echinoderms form a still more interesting study, for some of the Ceno-
manian genera do not occur in the Turonian, and of those genera which do
range upwards the representative species are for the most part different. It
is observable, however, that the different species of certain genera appear to
form correlative series, and to bear that amount of resemblance to one another
which We should expect if the newer had been gradually developed from the
older species under the influence of those causes which Darwin terms
** natural selection."

* Ann, Soc. GeoL Nord,, t. v., p. 442.

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140 GEOLOGY OF THE^ NEIGHBOURHOOD OP CAMBBIBGB.

The following is a list of the principal species belonging to these two
faunas : —

Lower Chalk.
Holaster subglobosus, Leske.
„ trecensis, Leym.
,, nodulosus, Gold/.
Hemiaster Morrisii, Forbes.
Epiaster crassissimus, lyOrb.
Cidaris Bowerbankii, Forbes,
„ vesiculosa, Goldf.
„ dissimilis, Forbes.
„ hirudo, Sorig (rare).
Pseudodiadema ornatum, Goldf.

„ variolare, Ag,

Ecbinocyphus difficilis, Ag.
Peltastes clathratus, Ag.
Salenia Clarkii, Forbes.
„ Austeni, Forbes.
Discoidea subucula, Klein.
„ cylindrica. Lam.

Middle Chalk.
Holaster planus, Mant.
„ coravium. Lam.
Cardiaster granulosus, Goldf.

„ pygnaoBus, Forbes.
Micraster oreviporuB, Ag.
„ cor-bovis, Forbes.
Cidaris subvesiculosa, D*Orb.
„ P dissimilis, Forbes.
„ hirudo, Sorig.
Cyphosoma simplex, Forbes.
„ radiatum, Sorig.

Echinoconus subrotundus, Mant,

„ globulus, Desor.

Saleniagranulosa, Forbes.

,, mespilia, Woodw.
Discoidea minima, Ag.
„ Dixoni, Forbes.

Many of the species which appear in the upper part of the Middle Chalk
range up also into the beds above the Chalk Rock, so that the greater
palseontological break appears to be that at the base of the Melbourn Rock ;
the following species, however, seem to have died out in England before or
during the formation of the Chalk Rock : —

Inoceramus Brongniarti, Sby,
„ mytiloides, Mant.

„ problematicus,ScAfo^.

Spondylus striatus, Sby.
Rhynchonella Cuvieri, D'Orb.
Ammonites (all the species

mentioned above).
Cidaris dissimilis, Forbes.
„ hirudo, Sorig.

Discoidea Dixoni, Forbes,
„ minima, Desor,
Echinoconus globulus, Desor.

„ subrotundus, Mant.
Holaster planus, Mant.
CyphoBoma simplex, Forbes.
Cardiaster pygmoeus, Forbes.
Salenia granulosa, Forbes.

Echinoconus subrotundus is a form which Prop* Forbes long ago recognised
as being " chiefly confined to a lower geological horizon than E. albogalerus, and
characteristic of the hard or lower chalk."* The same may be said of the aUied
but distinct species E. globulus, and both appear to be most abundantly developed
in the lower part of the zone of Terebratulina gracilis. The universal presence
of these and other Echinoderms in precisely homotaxial beds is a remarkable
proof of the constancy of these palaeontological zones over the Anglo-Parisian
province, and of the uniformity of the life-conditions that prevailed during this
period. — A. J. J-B,

2. Description op New Species.

Gasteropoda.

Scalariafasciata, Etheridge. PI. 1, Fig. 1.

Shell elongated or attenuated, whorls probably 12 or 14 (10 seenj, strongly
costated, ventricosq, and reticulated. Costae nodular where the concentric
striae pass over them, number of ribs or costa doubtful, probably 14 or 15.
Concentric striae numerous, well defined, about 18 on each whorl; between
each rib there are 6 or 8 faint vertical thread-like lines, giving the intercostal
or depressed spaces a reticulated appearance ; at the base of each whorl, or
along the sutural line or constriction an elevated rugose cord-like band (fascia)
is present, composed of wavy lines, so that there is no sharp or well-defined
depression between the whorls.

* Mem. Geol. Surv, decade iii. pi. viii.

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PAIi^ONTOLOGT. 141

This shell appears at first sight to be the species so well figured by Gold-
fuss,* we are now, however, able to add a few more (6) volutions to Munstbr's
fi^l^irre, and also show other characters not present in the German shell.
The sutural band is not present in the figure of Fusus costato-striatus, given
by GoLDFUss, even in a cast the place of this cord-like band would be con-
spicuous. Munstbr's specimen or figure, like our own, does not possess the
last or body whorl ; this is to be regretted, as we are therefore left without
evidence as to the nature of the mouth, consequently also the true name of
the genus is doubtful. Probably the last whorl was ventricose, and possessed a
nearly round mouth, if so, it would certainly ally it to the genus Scalaria, its
resemblance to that genus is striking, and but for the sutural band, should
determine it to be Scalaria dupiniana : that species, from the Gault of Folk-
stone and France, it is not, however, but very closely allied to it.

Whether this shell is really a Fusus, or a form of Scalaria, it is really difficult
to say, it certainly closely resembles the S. dupiniana^ D'Orb, out that
shell possesses no band or along the suture or junction of the whorls. The
absence of the body whorl and mouth is unfortunate ; reference to Gold puss'
figurej shows great similarity, but the whorls in our specimen are more ven-
tricose, being more constricted along the sutures, thus resembling the Gault
form, but the profound or deep sutures in the latter shell at once removes
it from the Gault shell. Sbalaria albensis, D'Orb, and S.Gaultina,D' Orb, \\
possess bands along the sutural line, but whether belonging to the top of the
one or base of adjoining whorl, am not able to say. This would probably be
a specific character.

Locality, Burwell (Totternhoe Stone). •

. Collection, Woodwardian Museum, Cambridge.

Turbo gemmatuSf Sow. Dixon, Geol. Sussex, p. 384, t. 27, f. 26.
This shell is figured by Sowerby in the above work, probably it is also the
species figured by S. Woodward, in the outline of the Geology of Norfolk in
1833, under the name of Cirrus striatus; the figure is so bad that strict
corelation or identification seems hardly justifiable ; it is, however, more than
probable that they are the same. Turbo gemmatus appears to be characteristic
of the Chalk Rock, and has been collected from most of the localities where
that zone is exposed.

Lamellibranchiata.
Pectenjissicosta, Etheridge. PI. 2, Figs. 1, la., and PL 3, Figs. 1, la.

Shell elongated, longer than wide, wings or auricles unequal, valves strongly
costated, or ribbed, costsB broad slightly arched or gently rounded, straight ana
about 15 in number, lines of* growth strongly marked, especially so with age,
appearing like two or three shells one within or placed upon the other.
The costae, or ribs of the upper half (ligamental portion) or two-thirds of the
shell have a line, or depression down the centre, giving them the appearance of
being double ; this character is not seen in the newer or last formed part of the
valve ; auricle of right valve deeply notched for bissal sinus, and waved in
structure. Hinge line straight, umbo pointed, intercostal or depressed spaces
half the width of the raised ribs or costae, and marked by slightly wavy lines
crossing at an angle of about 60°, occasionally they are zig-zag between the
3 or 4 of the central ribs, these Hues also cross some of the costae at the same
angle, on the anterior and posterior sides of the shell, but appear absent on
the middle costae, which are more flattened than the side ribs, and delicately
lined longitudinally.

The auricles difEer greatly, that of the left, or byssal side, being strongly
waved, deeply notched, and having corrugated parallel lines of growth.

This well-marked shell seems to have been overlooked, probably owing to
its rarity, or the want of good examples from other areas ; the Cambridge
shells from the Totternhoe Stone of Cherry Hinton and Burwell are, however,

* Petr. Germ.t. 171, f. 18.

J Pal. Fran. terr. cret., vol. p. 54, 1. 154, f. 10-13.
Petr. Germ. t. J71, f- 18, ^oc. cit.
§ Pal. Fran. terr. cr^t., vol. 2, p. 51, t. 154, f. 4, 5.
II Pal. Fran. terr. cret., vol. 2, p. 56, t. 154, f. 14-16.

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142 GEOLOGY OF THE NEIGHBOUBHOOD OF CAMBRIDGE.

admirably preserved^ and enable good characters to be given. Through the
liberality of Professor Hughe9> we are enabled to figure both valves of
this species (with many other fossils) from the fine collection in the Wood-
wardian Museum. We possess the left valve of the same shell from the
Lower or Grey Chalk of Dover, but badly preserved ; it is doubtless the Cherry
Hinton and fiurwell form.

The left valve of this specimen differs in manv respects from the right,
especially so as regards the costse which are much natter, and possesses the
impressed line or depression along the middle of the rib to the extremity or
ventral margin of the shell, as well as in the condition and structure of the
wings.

Hinge line straight, wings unequal, anterior largest and nearly double
the size of the posterior, marked with well-defined inclined costae, the ribs are
flatter and less rounded and elevated than in the opposite or right valve ;
again, the impressed line down the centre of the costae is constant to the
completeness of the shell in this valve, this and the flatness of the ribs readily
distinguishes one valve from the other.

Localities, Burwell, Cherry Hinton, and Orwell (Tottemhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Pinna tegulata, Etheridge. PL 1, Fig. 2.

Shell elongated, attenuated, wedge-shaped, umbones extremely pointed or
acute ; whole shell appearing to have been externally cancellated or angularly
fimbriated throughout, the fimbriae arching over the costse, being acutely
pointed in the centre of the costae. Numerous fine lines appear to have
occurred between the chief fimbriae. We figure the shell on account of its
acute form and peculiar costal markings, trusting that better specimens or
evidence may be obtained as to its external characters.

The acutely-pointed tegulate, or toothed character of the fimbriae, seems
peculiar to this shell. This character is not present either in P. tetragona. Sow.,
P. morcana, D'Orb., or P. decussata, Goldf. The nearest form to our shell is
Pinna quadrangulam, Goldf.?* but in that species the median line is falcate or
arched.

We have only an interior from which to diagnose the above characters, but
tl^e impression left on the chalk by the exterior of the shell and other characters
are sufficient to enable me to determine much of its original state, certainly
as to what it is not, for no European shell appears to resemble our form
sufficiently well to refer it to. No Indian or American species has any affinity
with the Burwell shell either as to form or marking.

Locality, Burwell (Tottemhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Inoceramus latus, Mant. var. Reachensis, Etheridge. PI. 1, Figs. 3, 3a.

Shell thin, flat, or very slightly inflated, regularly concentrically furrowed;
umbones very acute, the umbonal region rugose and wavy, hinge line straight
about two*thirds length of shell. Shell structure extremely thin, concentric
lines of growth very regular and sharply defined, intercostal striae or finer
lines of growth also very fine and arranged in shallow bands, which gradually
and equSly increase in width with the growth of the shell, the concentric
depressions being regular and smooth.

One shell resembles 7. latus, Mant., from the chalk of Sussex, alsoL mytiloides,
Mant., both these species are figured by Mantsll and Goldfuss, out with
neither of them can I correlate our shell. J. regularis D'Orb., is also closely
allied, but the sharpness of the ridge, acuteness and rugosity of the umbonal
region, and increased length of the hinge line removes it from that species;
and but for the sharpness or thinness of the hinge line and depth of the shell
it may be the L cuneiformis, D'Orb. After referring to all available or figured
species I am obliged to refer it to L latus, Mant., as the nearest species, and
give it the varietal name Reachensis, where, as at Burwell, it appears to be
somewhat plentiful.

Localities, Burwell (Tottemhoe Stone) and Reach (Chalk Marl).

Collection, Woodwardian Museum, Cambridge.

* Goldf. ^etr. Germ. 1. 127, f. 8.

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PALEONTOLOGY. 143

Inoeeramus convexus, Etheridge, PL 2, Figs. 6, 6a.

Shell, with both valves ventricose and expanded, nearly smooth or delicately
concentaically ridged; hinge straight about half the length of shell, containing
numerous shaUow vertical ligamental pits (30 or more). Umbones pointed,
contiguous, sHghtly curved, and Hues of shell growth coarser or more rugose
here than on the body of the shell. Right valve rather the smallest.

The shell, although resembling Ino. striatus, Mant., and some varieties of
7. Ltamarckii, Park., is nevertheless distinct from either, being more ventricose,
more finely striated concentrically, less rugose, and shell structure thinner.
I fail to find any shell agreeing with our Burwell form, therefore give it the
above name. The more numerous cartilage pits, narrow hinge area, and
extremely close growing concentric striae removes it from known Inocerami.
A slight ridge on the anterior side of the shell gives it some resemblance to
Liaia, but this character is much more strongly marked in the variety quad-
ratus from the same locality, described below.

Locality, Burwell (Totternhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Inoeeramus convexus, Ether., var. quadratus, Etheridge PI. 2, Fig. 7.

The specimen figured on Plate 2, Fig. 7, may be only a variety of Fig. 6
(J. convexus), but the strong ridge and large area on the anterior side is
here a significant character, provided it be a nonnal condition of the shell.
Shell ventricose, as broad as long, deep. Hinge-line probably nearly the
length of the shell. Umbones pointed, sub-anterior, slightly curved, and
more rugose or concentrically furrowed than the rest of the shell ; lines of
growth regular and equidistant. The concentric sulci or depressed areas
shallow, distant, and wide ; external layer of shell moderately thick.

The hinge line, ligamental pits, and posterior end are unfortunately not pre-
served in this shell, much of the wing being broken away ; it must, however,
have been of considerable dimensions, giving the shell when living a very
inequilateral appearance.

In some respects this shell resembles L Brongniarti, Sow., which again may
be taken for I. Lamarokiiy Mantell. This latter name, as applied to the figure
in Mantbll's Sussex, t. 27, f. 1, or Geol. Sussex, Dixon, New Ed. t. 63, f. 1.,
shows the area and length of hinge line, with hinge pits, 26 in number (not seen
in our shell). This want in the Burwell shell is unfortunate, and leaves us in
doubt as to the affiliation with the Sussex form. The large anterior area,
strong ridge, and concentric striae ally it closely to J. convexus of which I
believe it to be a variety. I name it L convexus, var., quadrata,

LocaUty, Burwell (Totternhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Inoeeramus {Mytilites) problematicus, Schloth., Petrif. p. 312.

Mytiloides labiatus, Brongniart, Geol. des Env. de Paris, t. 3, f. 4, p. 215.

Inoeeramus, D'Orb., Pal. Fran., Terr, cret, vol. 3, p. 510, t. 406.

Plate3, Figs. 9, 10,11.

Many specimens of a species of Inoeeramus have occurred to our collector
Mr. Allen, which are either the young of some mature form, or a small but new
species ; none of those in our possession are perfect, some mere fragments, one
or two, however, lead me to believe that tHey are young forms of Inoeeramus
problematictta, Schloth., D'Orb.,* J. mytiloides, Golaf.,t both of which appear to
me to be the same species. Inoeeramus {Mytiloides) labiatus, Brong., loe, cit,,
certainly is the same species ; but the two figures (Nos. 1 and 2) given by
D'Orb. on his plate (/oc. eit.) most closely resemble our specimens, so much so
that I am not justified in giving our fragments a new name. Young specimens
of L regularis,L>^Oth., would also much resemble those we possess.^: The French
shells occur in the middle beds of the 6tage Turonien, which equals our Lower
Chalk ; and therefore much upon the same horizon.

♦ Pal. Fran. terr. cr^t., p. 610, t. 406.
t Petr. Germ, t. 118, f. 4.
% Loc. dtf t 410.

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144 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

These fra^fments are figured as having value upon their stratigraphical dis-
tribution tliough the Chalk.

Localities, Missleton Hill near Fulbourn, and Chalk Hill> near Babraham
(from Middle Chalk, zone of Rhynchonella Cuvieri).

Collection, Museum Practical Geology.

Lima echinata, Etheridge. PI. 2, Figs. 2, 2a. 2b.

Shell very inequilateral, elongated, as broad as long, somewhat rhomboidal
in form, strongly ribbed, or costated. These costae are 24-26 in number, and
ornamented with two or three lines of closely set tubercles or blunt spines,
one central row, another on each side ; these give the entire shell a tuberculated
appearance ; hinge line straight, umbo rather acute, area under left wing small
and smooth, intercostal spaces deep and occupied by strongly marked transverse
lines.

I am unacquainted with any Ldma, British or foreign, at all approaching this
shell ; in shape it resembles L. Cottaldina, D'Orb., and L. parallela, D'Orb., and
in ornamentation the ribs resemble L. Cenomanensis, D'Orb., and L. granosat
Goldf., but none of these species are so tubercular or nodulose, and the inter-
costal striae differ from all.

Locality, Burwell and Cherry Hinton (Tottemhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Lima ornata, Etheridge. PL 3. Fig. 2, 2a.

Shell obtusely rounded, somewhat rhomboidal, umbo probably tumid ; ribs or
costae 16, roundly elevat;ed, and all ornamented by longitudinal lines composed
of small tubercles, intercostal spaces wider than the costal, or ribs, especially
BO on the posterior part of the shell where they are greatly developed, ana
densely decussated, or semi-tuberculated, the tubercles being arranged in lon-
gitudinal lines; umbones obscured or eroded; anterior portion of shell
rounded, posterior end or side truncated.

I have sought all sources, British and foreign, but fail to find anv shell re-
sembling this species either in shape or markings ; it was collected from the
Cambridge Greensand, unfortunately the hinge area is wanting on both speci-
mens, but the umbonal region was evidently deep or tumid ; the shell appears
to have been extremely thin or fragile.

Lima cottaldina, D'Orb., from the Gault (Aptifem) resembles our shell in many
respects, but the intercostal spaces in our shell are wider and decussated
instead of being nodular ; in shape, tumidity of the umbo, and probable small-
ness of the hinge line and wings, they are closely allied.

One of the specimens is preserved m a light coloured phosphate, the other
in a clayey marl, but both are from the Cambridge Greensand or Phosphatic
bed.

Locality Cambridge (Cambridge Greensand).

Collection, Woodwardian Museum.

Aviculafilata, Etheridge. PI. 2, Figs. 3, 3a.

Shell small, equivalve, inaequilateral, hinge line straight, as long as the
shell, ventral margin nearly circular, anterior side rounded, ventral valve deep,
especially so at the umbonal region ; valves marked by faint thread-like radia-
ting slightly wavy lines, 14-16 in number, ranging from the umbo to the
ventral margin, here and there these lines bifurcate, shell structure thin,
dense, and glazed.

In many respects this shell resembles the sub-genus MonotiSy Bronn, espe-
cially in its rounded anterior side. Pseudomonotis (OxytoiJia) semigldbosa of
the Arrioloow group,t resembles our shell both in the filiform striae and lines of
gro^^th which are densely arranged, as well as in general habit. The largest
example measures | of an inch in length by f in depth.

* Pal. Franc, Terr, cret., vol. 3, p. 537, t. 416, p. 5.
tPal. Indica, vol. 3, p. 402, PL 26, Fig. 1.

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PALEONTOLOGY. 145

The jafenus Peteria, Scopoli, may receive this shell, but want of internal
characters prevents our definitely determining this alliance.

Locality, Burwell (Totternhoe Stone). i

Collection, Woodwardian Museum, Cambridfj^e.

Avicula dubia, Etheridge. PL 2, Figs. 4, 4a.

Shell small, inaequilateral, ventral margin round, hinge line straight, longer
than width of the shell. Posterior side expanded, anterior side short, byssal
notch well defined.

The external portion of this shell is not seen, therefore unknown to me,
although placed upon the same tablet in the Woodwardian collection, with
Avicula filata, it certainly does not belong to that species. The shell is thicker,
stronger, and rounder in foim thou A. filata, again no byssal sinus is seen
under the anterior part of the hinge line of Av, filata ana the latter species
possesses a larger wing.

Small as this shell is, there is no doubt it is mature, and not a young form.
We have only two specimens, both interiors, one may be the lower and the
other the upper valve ; they appear to belong to the same species.

Localitjr, Burwell (Totternhoe Stone.)

Collection, Woodwardian Museum, Cambridge.

Spondylus cequicostatus, Etheridge. PL 2, Fig. 5.

Shell very insequilateral, rhomboidal, ventricose, densely costated, the costse
being all equal in size and gently waved, and about 80 in number, llie in-
terspaces are shallow, and about the same width as the costae, especially
near the centre of the valves. Umbo obtuse, hinge line straight ; area not
seen in our specimens, lines of growth irregular and general surface of the
shell wavy or undulating. The hinge area appears to have been small, about
one-third the length of the shell.

One of the specimens in the Woodwardian Collection shows along the
ventral margin of the attached valve a nearly vertical thickening at an angle
of 60°, which does not occur in the same valve of the other specimens ; but
for the peculiar habit of the shell, it might be taken for Lima or Hinnites ;
it is, however, too insequilateral for the latter genus, and the want of
symmetry removes it from Lima. The want of hinge line adds to the difficulty
of determination.

Locality, Cherry Hinton (in the zone of Holaster suh-glohosus above Tottern-
hoe beds and below the zone of Belemnites plenus or the Melbourn Rock).

Collection, Woodwardian Museum.

AnonUa papyracea, D'Orb., var. Burwellensis, Etheridge, PL 3, Figs. 3, 4.

Shell thin, inssquivalve, insequilateral, orbicular or rhomboidal, smooth or
nearly so,umbones rather acute and slightly rugose. Ventral margin rounded,
lines of growth on some specimens conspicuous. On one of the specimens
figured. Fig. 4, there are peculiar vertical lines running from the umbonal region
to the edge of the shell.

The above shell figured by D'Orbigny* closely resembles the Burwell form
in the Woodwardian Collection ; to so variable a shell I am compelled to give
a distinguishing varietal name.

No Anomia is mentioned or described from any part of the Chalk of Britain,
one species occurs in the Cambridge Greensand {Anomia transversa, Seeley), and
four species are known in the Neocomian, which completes the known species
from tne British cretaceous rocks. Their non-recognition from the true Chalk
is singular, and shows extreme rarity, as few formations have been more
extensivelv worked, or their fossil contents more carefully examined than the
Upper and Lower Chalk of England.

Our variety of D'ORBiQ^Y'd Anomia papyracea {A, Burwellensis) is, as usual
with species, and specimens in this genus, very variable in shape, and certain
markings on the shell may be due to attachment to other forms, therefore,

♦ Pal. Franc, Terr, cret., vol. 3. p. 755, t. 489, f. 7-10.
N309. K

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146 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBEIDGE.

as a rule, no value can be attached to them. We figure this species from the
Woodwardian Collection, Cambridf^e, as it seems abundant in the Tottemhoe
Stone at Bur well, and as being the only form known to us from the Chalk*
Neither Nillson or Romer name or figure any form of Anomia; Reuss, in
his Verstein. der Bohm Kreide, names and figures four species, but neither
are near our variety. The Southern Indian cretaceous deposits have yielded
biit one spe«es of Anomia (A. variata, Stol.) ; America, only 10 ; and all
Europe not more than 20 species.

Locality, Burwell (Totternhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Ostrea acutirostris, Nilsson, Petref. Succ. p. 31, t. 6, f. 6. PL 3, Figs. 5, 6.

Shell elongated, slightly curved, umbo acute, muscular scars elongated, ova
and large, a single elevated transverse ridge or triangular space occupies the
small area under the acute umbo, which is transversely striated, two lateral
projections or blunt teeth occur on both sides, and immediately under the area,
ligamental ridge minutely crenulated.

We have not the exterior of this shell so as to enable us to state with
Nilsson, " loc, cit.," that the " lower valve is radiately plicated and rugose, and
" that the upper or superior valve is also convex and rugose ; " nevertheless,
this shell can be no other than Nilsson's Ost. acutirostris. The figure given by
D*Orbigny* agrees tolerably well with Nilsson's description, both as to the
convexity of the upper valve and rugosity in both. We have not met with any
pubUshed notice of this shell in Britain, although it is said to have been
found in the Upper Chalk of Dover and Brighton. Nilsson, D'ORBiGNY,and
GoLDFUSS figure the species, but they all more or less vary in their delinea-
tions in the form of the shell, especially so in the umbonal region. The two
Cambridge specimens, which appear to be the attached valves, are the only speci-
mens known to me from that or any other area ; I therefore figure them in
order to draw attention to their probable occurrence. I feel by no means
certain that it is the shell, but they greatly resemble the form figured by
Nilsson and D'Orbigny,

Locality, Burwell (Totternhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Ostrea curvirostris, Nillson, var. inflexa, Etheridge, PI. 3, Figs. 7, 8.

Shell elongated, gently arcuated or curved, right valve slightly ventricose,
thick or deep near the umbonal region ; ligamental area in right valve, toothed
or crenulated for a short distance from the umbo ; shell moderately thick; the
right or upper valve is haliotoid in form, indeed strongly resembles the upper
valve of Exogyra haliotoidea, Sow. ; the markings that pass or occur across
the shell in the Cambridge Collection mav be due to attachment or growth
upon some other form as they are not distmguishable upon all the specimens
on the tablet.

Although our specimens do not quite agree with Nilsson's figures, yet
making allowance for the variation of growth in species of this genus, it
would be unwise to make the Cambridge specimens new species, probably both
th« true Ost, curvirostfis and Ost» acutirostris occur in the Burwell Lower
Chalk of the Cambridge area. The Cambridge shells are not quite so elon-
gated or acutely pointed as the form figured and described by NiLSSONf or
D'Orbigny.J There is, however, sufficient variation and difference to enable
me to give it the varietal name and also figure two specimens. Again, the
Burwell species are more tumid than Nilsson's, his form and figure being
more acute and longer; the figure given by Goldfuss§ is also more curved
and acute; the umbo not being so involute as in the Cambridge shell.
Messrs. Pictet and Campiech£|| figure D'Orbigny's species O. Rauliniana,

* Pal. Franc, Terr, cret., t. 481, f. 1-3.

t Petref. Suec, p. 30, t 6,f. 5.

X Pal. Franc., Terr, cr^t., t. 488, f. 9-11.

§ Petref. Germ., vol. 2, p. 24, t. 82, f. 2.

II Desc. Fobs Terr, cr^t., St. Croix, part 6, p. 307, t. 193, f. 15-16.

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PALiEONTOLOGY. 147

which very closely resembles our shell, more so, indeed, than the French as
figured on Tab. 471, Figs. 1-3, o£ the Pal^ontologie Frangaise ; to all these I
draw attention on account of the uncertainty of determination from few
specimens.

Localities, Burwell, Orwell, and Haslingfield (Tottemhoe Stone).

Collection, Woodwardian Museum, Cambridge.

Brachiofoda.
Rhynchonella Reederms, Etheridge. PI. 3, Fig. 12.

Shell oval, width equal to length, obtusely rounded, ventral valve flatter
than the dorsal, and thickened near the umbo, having also a broad but shallow
sinus, beak very small, acute, not incurved, dorsal valve more gibbous than
the ventra valve, foramen minute, round, surrounded by the small deltidium,
beak ridges sub-acute, almost obsolete, hinge line wavy, or gently undulating
ribs or costse about 20, 7 to 8 on the mesial fold, all e^ual sized or equally
developed along the frontal margin, apparently not divided or split as in
R, WoodwardL

This shell very closely resembles R. Woodwardi, Davidson,* but not the Tereb
galUna, Woodward,t which shell is much wider, more numerously ribbed, and
the beak much more acute than in our species. The extreme smallness and
acuteness of the beak and size of foramen serves also to distinguish it from
the above species and also from i2. Ctwieri.

Stratigraphically this is an important shell on account of its always occurring
in the Chalk Rock and in the few feet below. At the Reed and Barley Chalk
pits it is a characteristic shell, distinctly marking or determining the Chalk
Rock as a zonal horizon. This fact alone induces me to figure this form
regardless of its close affinity with R, Woodwardi, Dav.

Localities, Reed and north of Barkaway, and near Barley (Chalk Rock).

Collection, Museum of Practical Geology.

Terebratulina gracilis, Schloth., var. lata, Etheridge. PI. 3, Fig. 14.

Shell nearly orbicular, expanded, or broadly triangular, equal in width and
length, ventral or dental valve convex, the smaller or dorsal valve nearly flat ;
the ribs or costfie in both valves slightly ornamented by inbricating delicate
lines of growth, which arch over the ribs, giving them the appearance of being
nodulated ; alternating or intermittent ribs occur with the last growth of the
shell, there are about 22 chief or primary, and 8 smaller or shorter. This
variety appears to be confined to the Middle Chalk, and is particularly abun-
dant in tne middle zone of this division. That considerable difference and
variation occurs amongst the species of this genus there can be no doubt,
both as regards form and external characters, and this zoological difiPerence
has important stratigraphical value also, as this and other varieties in species
of the same genus serves to clearly determine zonal horizons over large areas.

It is difficult to distinguish this variety from the figure of T. gracilis given
by Mr. Davidson, J except that the number of ribs are greater in his figures,
and our specimens are flatter and wider.

We have a globose variety in the same beds, and the variety lata is the
T, gracilis of that zone, or the variety characteristic of it.

Localities, Middle Chalk, passim.

Collection, Museum of Practical Geology.

Terebratulina gracilis, Schloth. var nodulosa, Etheridge. PI. 3, Fig. 13.

Shell longer than wide. Beak area in ventral valve acute. Primary costse,
10 to 12 in number, densely and closely nodulated ; secondary costae, 6 to 8,
which are about half as long as the primary.

This nodulose variety contains fewer ribs, which are also more densely
nodulated than in the typical T. gracilis as figured by Mr. Davidson.§ Again,
in our specimens the dorsal valve is convex or globose, instead of flat as in Mr.
Davidson's figures.

* Brit. Cret. Brach., Pal. Soc., p. 77, 10, figs. 45-46.

t Geology of Norfolk, t. 6, f. 12.

J Cretaceous Brachiopoda, Pal. Soc., t. 2, f. 13-14.

§ Cretaceous Brachiopoda, Pal. Soc, p, 88, t. 2, f. 13-15, 1852-55.

K 2

Digitized by VjOOQ IC

148 GEOLOaY OF THE NEIGHBOURHOOD OP CAMBRIDGE.

This variety is confined to the Totternhoe Stone and part of the Grey Chalk
immediately above or overlying it.

Localities, Cherry Hinton and Burwell (Totternhoe Stone),
j Collection, Museum of Practical Geolof^y.

j Terebratulina striata, var., triangularis. Ether. PL 3, Fig. 15.

I Shell triangular in form, longer than wide. Beak tapering or acutely

j. rounded, hinge line straight. Foramen large, deltidium small. Beak ridge

|f indistinct, valves equally ventricose or convex, frontal margin broadly rounded,

i costae about 24, nearly half of which (or the secondary costae) are half the

length of the primary ; many of the chief ribs are split or divided on reaching
the ventral margin, lines of growth well defined.

This shell is very abundant in the Cambridge Greensand, and has hitherto
been considered as T. gracilis, var. rigida, of Sow. (M.C., vol. 6, p. 69, t. 636,
f. 2), also Davidson (Brit. Cret. Brach., Pal. Soc, p. 38, t. 2, fiF. 13-15). But
I have little doubt that it is rather a variety of T. striata, Wahl, and the
triangular form of this shell has suggested the varietal name.
Localities, near Cambridge, passim (Cambridge Greensand).
Collection, Woodwardian Museum, and Museum of Practical Geology.

Digitized by VjOOQ IC

PALEONTOLOGY.

149

APPENDIX B,

Lisr OF Gault Fossils (remanies) found in the **Cambbi3>ge
Grbensand." -

By A. J. Juk:es-Beowne..

This list is based upon that given in Quart Jouffi, Geol. Soc, vol. xxxi.
p. 305, supplemented by that in "vol. xjtxiii. p. 604, and by still later additions
and corrections.

Many species are included w>»ich have not yet been found elsewhere, because
their mineral condition is identical with that of the Gault fossils, and it is
thought that they have been derived from the same beds as their companions.

The fish remains have been identified by Mr. E. T.. Newton (see Catalogue
of Cretaceous Fossils in the Museum of Practical Geology, 1878).

The list of Reptiles includes only those species which have been fully
described, the names affixed to many specimens in the Woodwardian Museum
by Prof. Seeley not being inserted.

In the first column opposite the names, those species are indicated which
occur in the English Gault ; the second column contains those also found in
the Gault Sup^neur of France and Switzerland ; Dr. Barrois* recent memoir*
has enabled me to make some fresh insertions in this column.

The total number of named species of Invertebrata in this list is 215 ; of
these 122 are known also in the Gault of England, and 98 are found in
the Gault Superieur of France and Switzerland. The Vertebrata are 48 in
number.

English
Gault

Gault
Superieur.

AVES.

Enaliomis Barretti, Seeley.

„ • Sedgwickii, Seeley.

Rbptiija. "

Chelone (Bhinochelys) polchriceps, Owen.

„ „ (several species) - - ..

Crocodilus Cantabrigiensis, Seeley.

„ Icemcus, Seeley.

Ichthyosaurus campylodoD, Carter - - -

„ Walkeri, Seeley - - . .

Ornithocheirus ? Cuvieri, Bowerbank.

„ denticulatus, Seeley.

„ machsBrorhynchus, Seeley.

„ Sedgwickii, Owen.

„ simus, Owen.

„ Woodwardii, Owen.

Plesiosaums ? Bemardi, Owen.

„ constrictns, Owen.

„ latispinus, Owen.

„ Neocomiensis, Camp.

„ planus, Owen . - -

Polyptychodon interruptus, Owen - - - -

? Synyonosaurus macrocercus, Seeley.

♦ Ann. Soc. Geol. Nord,, vol. v. p. 227.

Digitized by VjOOQ IC

150 GEOLOGY or THE NEIGHBOURHOOD OF CAMBRIDGE.

Ganlt
Superiear.

Pisces.

Cimolichthys (Sanrocephalos) striatos, Ay,
Drepanophonis canaliculatus, Eg,
Edaphodon crassuB, Newton,

„ lamlnosus, Newton - - - -

„ Beedii, Newton.

„ Sedgwickii, Ag,
? Enchodus halocyon, Ag, - - ^ -

Hybodus sp. ----- -

Ischyodus brevirostris, Ag, - - - ,

„ latuF, Newton,
„ planus ?, Newton.
Lamna acuminata. Ag -

„ gracilis, Pictet Sf Camp, - - - -

„ plicatella, Beuss.

„ subulata, Ag, - - - - -

Lepidotus sp.

Otodus appendiculatus. Ag, - - . _

Oxyrbina macrorhiza, Pictet Sf Camp. - - _

? „ Mantelli, -^^r. ,

Facbyrhizodus glypbodus ?, Blake - - ,

Fisodas sp. ------

Fletbodus expansus, Dixon,

Fortbeus Gaiiltinus, Newton - - - -

FrotospbyrsBna ferox, Leidy, (Saurocepbalus lanciformis,
Ag,y not Harlan^ - - - - -

Ftycbodus spectabilis, Ag,
Fycnodus cretaceus, Ag,

„ paralleltts ?, Eg.
Spbenoncbus sp.

Cephalofoda.

' Ammonites auritus, Sby, - - - - -
„ „ var. Henauxianus, D^Orb,
„ „ var. Salter!, Sharpe,

„ ccelonotus, Seeley - - - -
„ ., var. yalbonnensis, Heh.
„ glossonotus, Seeley,

„ latidorsatus, Mich. « - - -

„ ■ planulatus, Sby, - - - -
„ „ var. Mayorianus, D*Orb,

„ Raulinianus, D*Orb, - - - -
„ „ var. tetragonus, Seeley, -
„ rbamnonotus; Seeley (= Gardonicus, Heb, -
„ „ var. sexangulatus, Seeley,

„ rostratus, Sby, - - . .
„ „ var. ? candoUianus, D*Orb,

„ „ var. inuatus, Siy. - - .

„ splendens, Sby, - - - .

„ „ var. cratus, Seeley - - -
„ „ var. leptus, Seeley,

„ Studeri, Pictet Sf Camp, - - „

„ Timothcanus, Mayor, - - - -

„ Vraconnensis, Pictet _ - - -
„ Woodwardii, Seeley.

Ancyloceras tuberculatum, Sby. - - - -

Anisoceras aimatum, Sby. - - - - ^

„ Saussureanum, Pictet - - - |

Baculites baculoides, D^Orb. - - - - i

„ (jrnudiniy Pict. Sf Camp.- - - - '

Beremnites minimuo, Lister - - . -

„ ullimus, I)' Orb. - , „ .

X
X

X ?

Digitized by Vj(Z)OQIC

PAL^ONTOLOaT.

151

English
Gault.

Gault
Sup^rieur.

Cephalopoda — cont,

Conoteuthis, sp.

Hamites intermedius, Sby. • - ' -

„ virgulattis, Pictet - - -

Helicoceras quadri-tuberculatum (?).

„ Robertiarmm, 2>*Or6. - - ■«

Nautilus alb^nsis, B'Orb, « - -

„ arcuatus, Desk, - - - -

„ clementinus, B^Orb. - - -

„ insequalis, Sbt/. ^ - - -

„ largilliertianus, lyOrb, - - -

„ MontmoUini ?, Pictet - - -

Scapiutes Hugardianus,Z)' Or6. - - -

„ „ var. Meriani, Pict Sf Camp.

,, var. simplex, Jukes-Browne

Turrilites Bergeri, Brongn. « - -

. „ elegans ?, JD'Or6. - - -
„ emericianus ?, V^Orb,

„ Hugardianus, D^Orb, - - -
„ nobilis, Jukes-Browne,

„ P|izosiamis, X>'Or6. - - -
„ Wiestii, Sharpe (var. Cantabrigiensis).

Gasteropoda.

Acmsea tenuicosta ?, Desk. « - -

„ „ var. tenuistriata, Seeley.

Aporrhais carinata, Mant, - - -

„ eiongata, Sby. - - - -

„ histochila, Gard,
„ marginata, Sby. .» - -

„ Parkinsoni, Mant, - - -

„ retusa, Sby. - - - -

,, „ var. globulata, Seeley.

Avellana Hugardianus, B^Orb, - - -

„ incrassata, Sby. - •- - -

„ ventricosa, Seeley.
Brachystoma angulare, Seeley - - -

Buccinum Gaultinum, D^Orb. - - -

Cerithium sp.

Cbenmitzia tenuistrata, Seeley - - -

Crepidula Cooksoni©, Seeley - . -

„ Gaultina, Buv. - - -

Dentalium decussatum, Sby. - - -

Funis elongatus, Seeley.
Fusus quinquecostatus, Seeley.

„ Smithii, Sby, - - - -

„ tricostatus, Seeley.
Gibbula levistriata, Seeley,
? Hipponyx Dixoni, Desk.
Littorina crebricostata, Seeley,
Natica Clementina, D*Orb. - - -

„ Gaultina, X)*Or6. - - - -

„ le^stnaia, JtikeS'Browne - - -

„ Rhodani, D'Orft. . - - -

Nerinaea, sp.
Nerita nodulosa, Jukes- Browne.

„ (Neritopsis) scalaris, Seeley,
Pleurotomaria AUobrogensis, Pict. Sf Roux.

„ Gibbsii, Sby. - - -

., * Iteriana ?, Pict Sc Camp. -

„ Jukcsii, Seeley.

„ La Harpii, Pict. ^ Camp. -

X X

X ?

X X

X
X
X X

Digitized by VjOOQ IC

152 GEOLOGY OF THE NEIGHBOUEHOOD OF CAMBBIDGB.

English
Gault.

Gault
Sup^rieur.

Gasteropoda— con<.

Pleurotomaria lima, D'Orb. _ . - _

;, regiiia, Pict. §• RoUx, : : -
„ Rhodani, D'Ori. : - - -

...

Rouxii, 2>'Or6. - - -

„ semiconcavd, Seeley.

„ VraconensiB, Pict. Sf Camp,

• *•

Solarium Carteri, Seeley.

„ dentatum, Desk. - _ - .

„ granosum, D'Orh, - - - -

„ omatum. Shy. ----'-
„ planum, Seeley,

„ Rochatianum, Pict. ^ Roux. - - -

...

„ Sedgwickii, Seeley.

Stomatodon politus, Seeley.

Tomatella pyrostoma, Seeley,

Trochus cancellatiis, Seeley (indecfBus, D*Orb,) -

Torbo Pictetianus, D*Orb. (nodosa, Seeley)

LAMBLLIBBANCinATA.

Area Hugardiana, D'Orb. - . - -

„ nana, D'Ori. . - - _ -

Avicula gryphffioides, Sby. . - . -

Cardita tenuicosta ?, Sby. . - --

CucullflBa glabra. Park, - - . -

Exogyra conica, Sby. - - - - . -

„ „ var. plicata, Sby.

„ Rauliniana, D^Orb, - - - -

Fimbria Gaultina, Pzct -

...

Gervillia solenoides, Defr.

Inoceramus concentricus. Park, - - - -

„ sulcatus ?, Park, - - - -

Isoarca Agassizii, Pict. Sf Roux, - - - .

• ..

Leda solea, X)*Or6.

Lima elongata, Sby, - - - - -

„ globosa, 56y. - - - -. -

„ inteT\mea.t&, Jukes-Browne.

„ Rauliniana, D*Orb. - - - - . -

Luclna tenera, Sby. - . - - .

Nucula Albensis, X>'Or6.

„ bivirgata, Sby. - - - - -

„ oTata, Mant. - - - - c -

„ rhomboidea, Seeley,

„ subelliptica, Seeley,

„ vibrayeana, J)' Orb.

Ostrea frons, Par^. . - - - -

„ vesicularis, Sby, - - - - -

Pecten aptiensis, B^Orb., var. Barretti, Seeley -

...

„ orbicularis, Sby. - - - - -

„ RauliniaDU8,2>' Or6. . - - -

„ subacutus ?,Z>*Or6.

„ (Neithea) quadricostata, Sby.

„ ( „ ) quinquecostata, Sby. - - -

„ (Hinnites) pectinatus, Seeley, M. S.

„ ( „ ) Studeri, Pict 6f Roux. -

„ ( „ ) trilinearis, Seeley.

Perna lanceolata, Geintz - - . -

„ oblonga, Seeley.

„ Rauliniana, D'Orh. - - ^ -

„ semie Uptica, Seeley.

„ subspathulata, Reuas - - - -

Digitized by VjOOQ IC

. PAIi^lONTOLOGT.

153

English

Gault

Gault.

Sup^rieur.

Lahellibbanchiata — cont.

Fholadomya decussata, Sbtf., var. iriangularis, Seeley

•J
?

Plicatola pectinoides. Shy, - - _ >

„ sigiUina, Woodward - - - -

Spondylufl gibbosng, Z>»Or6. -

Tellina phaseolina, PicU Sf Camp, - - -

Teredo sp.

Bbachiopoba.

Kingena lima, I>efr. - - - - -

Bhynchofiella dimidiata, Sby, ....

...

„ „ var. convexa.

„ sulcata. Lam,

Terebratula biplicata, Sby,, var. Dutempleana, D'Orb. -

„ „ var. obtusa, Sby,

CRtJSTACaBA.

Cyphonotus incertas. Bell.

Dianlax Carteriana, JBell - - - - -

Etyus Martini, ilf ant.

„ similis, Bell,

Eucoryetes Carteri, McCoy,

Glyphsea Carteri, Bell,

„ cretacea, McCoy - - - -

Hemioon Cunningtoni, Bell,

Homolopsis Edwardsii, J9e// - . . ^

Hoploparia scabra, B^l ....

„ sulcirostris, ^eff . . - .

NecrocarcinuB Beechii, Dedong, • . . .
„ tricarinatus, Bdl - - - -

„ Woodwardii, ^e// - - - -

Falffiocorystes Stokesii^ ManU - . . .

Phlyctisoma granulatum. Bell,

„ taberculatum. Bell,

Scillaridea cretacea, Seeley, M, S,

Squllla McCoyi, Sedey, M. S.

Xanthofia granulosa, McCoy,

Serpula antiquata, Sby, - • - - .

Serpnla plexus, Sby, - - - - .

ECBINODERMATA.

Cidaris Gaultina, Forbes .....

Gralerites castaneus?, ^roR^.

Hemiaster M*Coyi, Seeley . - . .

Hemipneustes sp.

Bolaster Isevis, Beluc, . . -

«••

Pentacrinn8Fittoni?,-4««^ . . . .

Fsendodiadema Barretti, Woodwd,

„ Carteri, Woodwd,

„ fuogoideum, Seeley,

„ intertubercnlatum, Seeley.

„ inversum, Seeley.

„ omatum, Gold/.

„ scriptum, Seeley.

„ variolare, Brong.

Salenia sp.

Digitized by VjOOQ IC

154 GEOLOGY or THE NEIGH BOUBHOOD. OF CAMBRIDGE,

English
Ganlt.

Gault
Saperiem*.

ACTINOZOA.

Isastrsea sp. - - -

Trochocyathus angulatus, Dune. -
„ conulus, Edw,

„ Harveyanus, Edw,

SPONGIDiB.

Acanthophora Hartogii, SoUas,
Bonneyia bacilliformis, Sollas

(and four other species, Sollas),
Brachiolites tubulatus, Smith,
Cephalites Benettise, ManL

,f capitatos, Smith,

,y compressus, Smith.

„ guttatas, Smith
Eubrachus clausus, Sollas.
Hylospongia Briinii, Sollas

(and two other species, Sollas).
Fharetrospongia Strahani, Sollas.
Polyacantha Etheredgii, Sollas -
Betia costata, Sollas

„ simplex, Sollas
Bhabdospongia communis, Sollas -
Ventriculites ewvsLtaB,Smith.

y, mammillaris, Smith.

„ quincuncialis. Smith-

„ texturatus, Goldf.

Parkeria compressa. Carter,
? „ nodosa. Carter.
? „ sphsBTica, Carter,

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WELL SECTIONS. 155

APPENDIX a

WELL SECTIONS.

[Where not otherwise stated these are in Sheet 51, S.W.]

CAMBRIDGESHIRE.

1. Babraham. Worsted Lodge. Cottages.

Communicated by Mr. H. Tomlison, C.E.

128 feet above Ordnance datum.
Water stands 58 i feet from surface.

Chalk •• •• « ■ «> ••65 feet.

2. Balsbam. Parish well.

Communicated by Mr. H. Tomlison, C.E.

387 feet above Ordnance datum.
Water stands 175 feet from surface.
Boulder Clay and Chalk - - - - 275 feet

3. Balsham (2 miles N.W. of) Dotterel Hall.
Sunk 162 feet, the rest bored.
White Chalk with Greyish Chalk at bottom - 309 feet.

4, 5. Balsham (2 miles W, of) Gunner's Hall.
295 feet above Ordnance datum.
At the Farm, water stands 219 feet from surface.

Boulder Clay and Chalk - - - 229 feet.

At the Cottages, at a lower level : —
Chalk 175 feet.

6. Barnwell. The large Brickyard.

Communicated by Mr. Lee.

Shaft 20 feet, the rest bored.

Feet.
[Chalk Marl] Soil and white clay - - - 10
[Gault] Blue clay 150

7. Barrington.
Communicated by Mr. N. W. Johnson.

Feet.
Gault ------ about 160

"Rock" and sand 5-10

155 to 160

8. Barrington. Coprolite works, west of Church.

Four or five wells, varying from 70 to 125 feet in depth. In one the
water overflows at the surface, in others it stands at varying depths down to
25 feet.

Digitized by VjOOQ IC

156 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBRIDGE.

9. Barrinoton. Coprolite-works, three-qaartera of a mile E. by N. of tlie

Church.

Water overflows.

Feet.

Chalk Marl - 16

Gault and Lower Greensand - - - - 185

10. Barton. A quarter of a mile N. of the Church.

Communicated by Mr. N. W. Johnson.

Shaft, 55 feet, the rest bored.

Water rises to within 38 feet of the surface.

Feet.

Chalk Marl - - 22

Gault 113

Rock - . • 9

144

14. BOTTISHAM.LOAD...

Communicated by Mr. Flavell.

Feet.
Earth and white clay [Chalk Marl] - - - 21

Blue clay [Gault], rocks and sand ... 130

151

12. BOTTISHAM FbN.

Communicated by Mr. Flavell.

Feet.
Black earth- ------ 4

[Chalk Marl J, white clay - - - -

[Gault i^nd ? Lower Greensand], blue clay, rocks and
sand - - - - - . 130

142

Another version of this well shows :

Feet.
Bored through Gault and Greensand - - - 120

Dug down to eoprolifes *- "- *- "- 10
^ ,, Ga ' '^

130

13. BoTTisHAM Sluice.

Gommumcated by Mr. Flavell.

Feet.
Black earth ------ 5

Blue clay [Gault] - - - - - 120

Rocks and sand - . - • - - —

14. Bourn, near (3 miles S.S.W of Elsworth).
Prof. H. G. Seklby. Ann. and Mag. Nat^ Hist. ser. 3, vol. x. p. 100.

Feet.

Hard blue clay 84

Alternate bands of stone and sand, \cith a layer of ex-
tremely hard grey-blue rock - - - - 14
? Blue clay to bottom of well - - - - 52

150

Digitized by VjOOQ IC

WELL SECTIONS. 157

. 15. Caldecote. Mr. Westrope's.

Sunk 27 feet, the rest bored.

Water stands 17 feet from the surface.

Gault(? and Boulder-clay) - - - 67 feet.

. The bore-hole ends in the top of a hard rock.

16. Cambridge. Bateman Street. (Mr. H^dley's.)

Feet.
Soil and clunch [Chalk Marl] - - - 16

[Gault] blue clay to Greensand and water - - 120

Another account of this well gives the thickness of the Gault as 160 feet.

17. Cambridge. Coprolite Works near the Observatory.
Communicated by the foreman.

Feet. -

Gravel 12

Chalk Marl 12

Gault to rock 120

144

17a. Cambridge. Cemetery.
Gault to rock - - . . . 130 feet.

18. Cambridge. East road and New Town generally, the wells are, as

below.

Communicated by Mr. Coulson, Builder.

Feet.
Gravel - - - - - - 10 to 20

Gault about 130

Sand and rocky beds - - - - 5 to 10

146 to 160

19. Cambridge. Coldham's Common.
Communicated by Mr. Flavell.

rChalk Marl] soil and marl -. • - - 27

[Gault] blue clay - - - - - 120

[Lower Greensand], clayey sand and " rock '' - 10

"l67

20. Cambridge. Coldhams Common.
Communicated by Mr. Coe.

Feet.
[Chalk Marl] soil and marl - - - •» 18
[Gault] blue clay 107

125

21. Cambridge. Coldhams Common. Coprolite works on northern side.
Communicated by the Foreman.

Feet.

Chalk Marl 10

Blue clay (bored) - - - - - 120

130

Digitized by VjOOQ IC

158 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBRIDGK.

22. Cambridge. Coldhams Common, N. side.

Communicated by Mr. Lee.

Feet.
[Chalk Marl] white clay - - - - 10

[Gault] blue clay 130

Pock i

140i

2X Cambridgk. Coldhams Common. Coprolite works, a quarter of a mile

S. of.

Communicated by Mr. Coe.

Feet.
[Chalk Marl] grey and blue marl - - - 2o

rQjx-| r Blue clay - - - - - 110

'- -' L Dark clayey sand and coprolites - - 6

[Lower Greensand] hard rock - - - 1 1

150

23. Cambbidgb. Hills Road (Mr. Thoday's).

Communicated by Mr. Flavell.

Feet.
[Chalk Marl] soil and clunch - - - 20

[Gault] blue clay 160

Black sand and rock - - - - - 20

200

This well is exceptionally deep, and Mr. Thoday states that alternations of
hard and soft beds were met with below the Gault. The thickness of the
latter is also doubtful.

25. Cambridge. Railway Station.

Communicated by Mr. Flavell.

Shaft 60 feet, the rest bored.

Feet.
Gravel and clunch - - - - - 20

Gault, with coprolites, at 40 feet down - - 120

Sand, a few feet - - - - - —

140+

26. Another well given as at the railway, probably at Mill Road level-crossing :

passed through—

Feet.

Gravel 6

[Chalk Marl] white clay - - - - 20

[Gault and Lower Greensand] blue clay, rocks and
sand .-..-. 130

156

Digitized by VjOOQ IC

WELL SECTIONS.

159

27. Cherry Hinton. Cambridge Waterworks. Originally 46 feet ;
deepened in 1875.

Communicated by Mr. H. Tomlison, C.E.

Shaft to the Gault, the rest bored.
' Water within a few feet of the surface.

Soil and light-coloured marl . - -

Darker clunch - - - - -

Light-coloured clunch or marl - - -

Greyish chalk - . - . -

LBlue clunch, with coprolite bed at bottom
Slate-gr^ clay, with a band of small grey copro-
lites 33 feet from the bottom - - -

{Brown clayey sand, with ferruginous phosphate
nodules at bottom, and a hard rock below -
Soft brown sand with water . - .

[Chalk Marl,
48 feet.]

Gault.

[Lower

Feet.

6
23

•

4
8

125

"l76

28-30. Cherry Hinton. 1. Cottage opposite the Robin Hood. 2. Bishop's
Charity Farm. 3. Hill's Charity Farm.

Communicated by Mr. H.

Tomlison,

C.E.

Height above Ordnance datum
AVater level, below surface
Depth of well in chalk

55
40

167
126
132

171
129
132

31. CHBfJTERTON.

Communicated by N. W. Johnson.

[Valley Drift] gravel and sand

[Gault] blue clay -

[Lower Greensand] rock and sapd

Feet.

- 10

- 105

123

32. CONINGTON. (51 N.W.)
Seeley. Ann. and Mag. Nat. Hist. ser. iii. vol. x. p. 103.

Blue clay - - - -

Hard rock ------

Blue clay ------

To rock, yielding a small supply of salt water -

Feet.
100
5
145

250

33. COTON.

Communicated by Mr. Flavell.

[Chalk Marl] soil and white clay -
[Gault] blue clay - - -

Lower Greensand] rocks and sand -

Feet.

120

131 -f-

Digitized by VjOOQ IC

160 GEOLOGY OF THE NEIGHBOURHOOD OF GAMBBIDGE.

34. CoTON. Wells at Coprolite worka.

Commanicated by Mr. N. W. Johnson.

Feet.

Gault 120 to 130

Rock and sand - - - - m S „ 12

35. COTTENHAM. (51 N.W.)

Communicated >y Mr. Plavell.

Feet.

Black earth 4

Blue clay, mixed with rock - - - - 200

Rock and sands - - - - - - —

36. Dry Drayton. Scotland Farm.

Sunk 114 feet, bored 30 feet.
Water, 100 feet from surface.
Boulder Clay and Gault.
The wells in the lower part of this village are 50 feet deep, in the upper part
by the rectory, 180 to 190 feet.

37* EvBRSDEN. Coprolite Works.
Communicated by Mr. N. W. Johnson.

Feet.

Gault 125 to 135

Lower Greensand, rock and sand - - - 10 „ 15

135 „ 150

38. EvKRSDEN. The Quarry.

Water, 64 feet from surface.

Chalk 72 Feet.

39. Fkn Ditton. Coprolite Works.

Communicated by Mr. N. W. Johnson.

Feet.
ChaJk Marl] white day, varies firom - -> 3 to 30

;Gault] blue clay 108 „ 120

ILower Greensand] rock and sand, varies from - 9 „ 12

» 40. Fbn Ditton. Plough Inn.

Feet.

Clunch - 20

Gault 110

Rock and sand • - - - - 10 or 20

41. FuLBouRN. County Asylum.

Communicated by Dr. Bacon (Medical Superintendent).

Shaft throughout, water rises to 56 feet from sur&ce.

Feet.
Clunch - - - - - - - 594

42-44. FuLBOURN. 1. Fulboum Mill, W. of the village. 2. FulboumLodge.

3. Fulboum Valley Farm.

Communicated by Mr. IL Tondison, C.E.

Height above Ordnance datum

Depth ofwell in chalk . . .

Water level, below snrfiMse • . .

110
76

158
117
114

100
56
53

Digitized by VjOOQ IC

WELL SECTIONS. 161

45. GiRTON- Inn near the Rectory.

Sunk 33 feet, the rest bored.

Feet.
Gravelly soil ------ 3

Blue clay [Gault] 50

Clayey sand and greensand - . - " ?

Rock, with water - - - - - - 1

46, Hardwick. Whitwell Farm.

Communicated by Mr. Flavell.

Feet.

[Chalk Marl] soil and white clay - - - " ,?5

[Gaultjblue clay . - - - - - - 110

[Lower Greensand] rocks and sand - - - —

47. Harlton. Coprolite works.

Communicated by Mr. N. W. Johnson.

Feet.
Gault ' 125 to 135

Lower Greensand, rock and sand - - - 10 „ 15

48. Haslingfibld. Coprolite Works.

Communicated by Mr. N. W. Johnson.

^ Feet.

Gault ^^^*^^ft

Lower Greensand, rock and sands - - - 9 „ 18

48a. Haslingfibld. Coprolite Works near Cantalupe Farm.
Obtained from the foreman.

Feet.
Clunch [Chalk Marl] - - - - - ,20

Blue Clay to rock [Gault] - - - - 130

160

49. Haslingfibld. Daintrees Inn.

Sunk 33 feet, the rest bored.

Feet.
Gault, Blue clay, sandy at bottom - - - 153

Lower Greensand, sand, &c. - - - - 20

173

50. Haslingfibld. Near the Church.

Commumcatea by Mr. Pond.

Feet.
Clunch with coprolites at bottom - - - - 14

FGaultl clay with coprolites (and Ammonites interruptus) at

bottim . . ■ . ■ . ■ ■ " ^^Q

[Lower Greensand] rock and greensand - - - ^

"l57
N309. ' L

Digitized by VjOOQ IC

162 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBBIDGE.

51. Hatlby St. George (52 S.E.)

Communicated by Mr. H. Tomliaon, C.E.

Sunk 170 feet, the rest bored.

Water rose within 140 feet of the surface.

Feet-
Clay with chalk stones [Boulder Clay] - - - 120
Gravel (chalk, flints, and pebbles) - - - 28
Gault (clean blue clay) ----- 22
Greensand ------ 30

200

52. HisTON- Fruit Mills, by the Railway Station.

Feet.
Valley Drift] gravelly loam - . - - 5

;Gault] blue clay ------ 60

Lower Greensand] rock and sand . - - 5

53. HoRNiNGSBY, near Highball Farm.

Communicated by Mr. R. Piggot (Guilden Morden).

Feet.
Soil and White Clay [Chalk Marl] - - - 15

Blue clay [Gault] 120

Rock and sand [Lower Greensand] - - - 10

145

54. Kingston, Parish well.

Sunk 89 feet, the rest bored.

Water within 65 feet of the surface.

Feet.
Gault (and Lower Greensand?) - - - - 189

55. LoLWORTH. Cottage, a mile east of village.

Sunk 35 feet, the rest bored.

No supply, but bore fills in at the bottom when lefi; for a few hours.

Dark [Kimeridge] clay, with bed of rock 30 feet from surface, and at every

few feet below - - - - - - -135 feet.

56. Madingley.

Communicated by Mr. Flavell.

Feet.
Soil 3

t Chalk Marl] white clay, with coprolites at bottom - 14

(Jault and Lower Greensand] blue clay, rocks and sand - 140

I57

57. Madingley Road.

Communicated by Mr. Flavell.

Feet.
Sijil and gravel ------ 7

[(]Jhalk Marl'l white clay, with coprolites at bottom - 6

[Gault] blue' clay - 120

[Lower Greensand] rocks and sand ^ - - —

Digitized by VjOOQ IC

WELL SECTIONS, 163

58. Meldreth. By the Church.

Water overflows.

Feet.
Chalk and Gault - •« • •• said to be 300

58a. Meldreth^ Railway Station.

Communicated by Mr. F. J. Carver (Whaddon).

Water overflows.

Feet.
'Chalk Marl] White clay, to coprolites - - - 60

[Gault] Blue clay 240

[Lower Greensand] Rock - - - - about 6

305

58&. Meldreth, about a mile N.W. of the Railway Station,

Conmiunicated by Mr. F. J. Carver (Whaddon).

Feet.
[Chalk Marl] white clay - - - - - 30

Gault 210

[Lower Greensand] rock ----- 8

248

59. Orwell. Coprolite works, S.E. of.

Water, 20 feet from surface^

Feet.
C/lunch and Gault 180

60. Over. (51 N.W.)

Communicated by Mr. Flavell. No water.

Feet.
Black earth and gravel - - - - - 15

Blue [Oxford] clay, with chalk-stone and black rocks - 200

215

60a. Pampisford. Mr. C. Scruby's Brewery.

Sunk and communicated by Mr. J. Ingold.

Water-level 6 feet down, sustained pumping of from 40 to 50 gallons a
mmute. [Supply probably derived from the Tottemhoe Stone.]

Feet.

Garden mould - - - - - - 3

'Soft white chalk 7

Hard white chalk - - - - 16

„ „ with soft layers - - 5

Hard chalk - - - - - 13

Soft grey chalk, with hard piece of chalk at bottom 69
Very soft chalk - - - - - 5
Soft chalk, with hard piece at bottom - - 1

, Soft chalk 64

[Middle

and ,
Lower
Chalk].

125i
L 2

Digitized by VjOOQ IC

164 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBRIDGE.

61. Sawston. Borough Mills.

The left hand column of figures from particulars and specimens preserved
at the Mills. The right hand column communicated by Mr. G. Ingold.

The water comes in from upper part of the Lower Greensand, and rises to
14 feet below the surface, at about 16 gallons a minute. The water is impreg-
nated with salt.

Feet.

Feet

Made ground - - - - - —

Chalk, at 47 feet a bed of flints with much water 145

150

Gault 167

150

Lower Greensand - - - - ^ 65

? Kimeridge Clay - - - - —

—

377

62. Shelford. Mills by Railway Station.

Coarse gravel - - - - -

Clunch, with coprolite-bed at bottom

Blue clay ------

Soft bluish earth (" bear's muck ") - - _

Brown quick-sand - - - - "

Dark grey ironstone rock - - - -

Feet.
10
90

170

2
6
2

280

Chalk

63. Shelford. Heath Farm.

156 feet above Ordnance datum.

Communicated by Mr. H. Tomlison, C.l

Water stands 96 feet from surface.

Feet.
102

64. Shelford. lime Kilns, by Little Hill Inn.

119 feet above Ordnance datum.

Communicated by Mr. H. Tomlison, C.E.

Water stands 71 feet from surface.

Chalk

Feet.
75

Chalk

65. Shelford. Red Cross.

69 feet above Ordnance datum.

Communicated by Mr. H. Tomlison, C.E.

Water stands 254 feet from surface.

Feet
32

Chalk

6G, Stapleford. Windmill. .
About 120 feet above Ordnance datum.
Water stands 53 feet from surface.

Feet.
63

Digitized by VjOOQ IC

WELL SECTIONS. 165

67. Strbatham Fen. Dimmock's Cote (51 N.W.)

Communicated by Mr. FlaVell.

Feet.

Black earth 3

Peat - . - - - - - - 18

Blue [Kimmeridge] clay - - - - -110

Rock and sand .----- 10

141

68. Strbatham Fen. Mr. Feust's Farm (51 N.W.)

Communicated by Mr. Flavell.

Feet.
Sand and gravel ------ 12

Blue clay 18

Rock and black sand " - - - - - —

69. Swaffham Bulbeck, Longmeadow.

Communicated by Mr. Isaacson.

Feet.
[Chalk Marl] clunch, with coprolites at bottom - - 42

[Gault]Clay - - . • . " . -112

[Lower Greensand] rock and greenish sand, with small
pebbles of quartz - - - - - 15

169

69a. Swaffham Bulbeck, Longmeadow Farm. (North of.)

Feet.
[Chalk Marl] soil and ciialk - - - - 15

[Gault^ clay ^ -^ -•-.. - - nearly 120

[Lower Greensand] ropk and greensand - - about 30

165

69b, Swaffham (Prior?).

Communicated by Mr. Flavell.

Feet.
[Chalk Marl] soil and white clay- - - - 83

iGault and" Lower*Greensand] blile clay, rock and sands- 120

. - - 203

70. Trumpington. Mr. Sayle's.

Communicated by Mr. Thoday.

Feet.
Clunch, with coprolites at bottom - - - 35

[Gault] blue clay 140

[Lo\^er Greeiisand] rock and sand - - - 20

195

71. Trumpington. Mr. Whitmore's.

Feet.
Soil and clunch, with coprolites at Lottoiii - - 36

[Gault] blue clay with vein of large coprolites 55 feet

from the bottom - - - - - 136

[Lower Greensand] greensand and water - - 3

"T75

Digitized by VjOOQ IC

166 GEOLOGY OF THE NEIGHBOURHOOD OF CAMBRIDGE.

72, 72a, h. Vandlbbury. 1. Duke of Leeds' garden. 2, Lodge half a mile

E. of. 3. Cot Farm, a mile to S.E.

Communicated by Mr. H. Tomlison, C.E.

Height above Ordnance datum - - -
Depth of well in Chalk - - - -
Water level from surf ace - « -

247
206
199

147

97
91

113
60
54

73. Watbrbbach.
Communicated by Mr. Flavell.

Black earth - - - ^ -

Blue clay [Gault] to rock and sand

74. Watbrbbach Fbn, Chitering Hfll ? (51 N.W.)
Communicated- by Mr. Flavell.

Black earth - - - « .

Gravel ------

[Gault] blue clay - - - - -

Lower Greensand] rock and sand

Feet.

4
120?

Feet.

75. Wbndy. CoproHte Works S.E. of.
Water overflows.

[Gault] dark clay -
[Lower Greensand] | j^i^

Feet.
115

120

76. Whaddon. Coprolite Works.
Communicated by Mr. F. J. Carver (Whaddon).

Feet.
Chalk Marl to coprolites - • - • 5 to 30

Gault clay - - - • - - 150 to 175

Rock [Lower Greensand] - - - - 5 to 10

160 to 215

77. Whaddon. Coprolite Works near King's Bridge, one mile N.E. of.
Communicated by Mr. H. Tomlison, C.E.

Feet.

Chalk Marl 15

Gault and Rock at bottom - - - ■• * 110

78. Whaddon. Well at Mr. F. J. Carver's house.

Communicated by R. Piggott (well-sinker).

Water overflows.

[Chalk Marl] to coprolites - - - -

Gault clay -------

[Lower Greensand] rock and sand, punclitd

125

Feet.

17
171

198

Digitized by VjOOQ IC

WELL SECTIONS.

167

79. Whaddon. West of Church, and in front of the Inn,
Water overflows.
Clunch and Gault, said to be 200 or 300 feet.

80. WicKBN. (51 N.W.)
Communicated by Mr. Flavell.

Feet,

Soil

« M ■

Blue clay -

•

Black rock

< m

Blue clay -

•

Black rock

Blue clay -

■ M t

Similar alternations for

■ M «

. 178

200

81. WiMPOLE, Coprolite Works.

[Gault] blue clay - - - - -

[Lower Greensand] rock and sands, varies — about

82. WiMPOLE. Coprolite Works, near The Ruins.
Sunk 120 feet, the rest bored.
Water, 80 feet from surface.

Clunch and Gault ■--,.•

Feet.

3 75

187

Feet.
180

HERTFORDSHIRE.

83. GuiLDEN MoRDEN. Coprolitc Works W. of. (46 N.E.)

Communicated by H. G. Fordham, Esq.

Sunk 52 feet, the rest bored.

Feet.
Chalk Marl, with coprolites at bottom - - - 20

Gault, with bed of coprolites a few feet from the bottom - 172

192

HUNTINGDONSHIRE.

84. Bluntisham. Mr. Tebbuts. (51 N.W.)
Very little water ; drains in from hard beds.

Oxford clay, with hard bands - * •

Feet.
300

Digitized by VjOOQ IC

168 GEOLOGY OP THE NEIGHBOURHOOD OF CAMBBIDGE.

APPENDIX D.-BORINGS.

CAMBRIDGESHIRE.
Chesterton. N.E. of the Ferry. Trial boring.

From a MS. book of Bections in the 'Office of the Ge'ological^ Survey, Jermjm
Street, London;

•••*'• Feet.

Made ground •--- -- - 4

Black peat - ' 2

f Hard gravel - - - - 2

[VaUey Drift] ^White gravel - - - - 4

L Shingly gravel - - - - 4

[Gault]* blue clay 5

Rampton." Side of road to Willingham, probably near the Church.
Trial boring. (51 N.W.)

From a MS. book of sections in the Office of the Geological Survey, Jenny n
Street, London.

^ Feet.

"Solid brown clay, with a white stone - 4

White rock and gravel, very hard - 2

Coloured clay - - - - 2

Blue clay, streaked with white and small

^« spots -of talc {selenite] - - 3

Oxford Qayt^

Willingham and Bluntisham. (51 N.W.)
From a MS. book of sections in the Office of the Geological Survey, Jermyn
Street, London.

No. 3.— By the side of the River Ouse [probably by the Hermitage].

Feet.
Brick eaJth " - - - - - - 2

Black bog -------5

Black peat, rather stiff ----- 2

■ gravel, mth sand - - - - 11

Blue [Oxford] clay to H

21J

No. 4. — North of the above* between the *-^01d and New Bedford Levels **
(i.e., between « The Washes ").

Feet.

Clay - - M - 2i

Sand and clay ------ 7i

Gravel and sand ------ 2

Blue [Oxford] clay 4

* Wrongly marked as Kimeridge Clay in the Memoir on the Geology of the Fen-
land, p. 254.

t Wrongly marked as Boulder Clay in the Memoir on the Geology of the Fenland,
p. 146.

Digitized by VjOOQ IC

BORINGS.

169

No. 4a, — Earith Wash. Further N. or N.E. in similar situation.

Feet.

Yellow clay ------ 5

Black peat 18

Loam and sand ------ 2

Loam and flint ------ 2

Gravel, sand, and stone - - • - - - 3

Blue [Oxford] clay 1

No. 4^. — Still further N.E^, in similar situation.

Yellow clay
Black peat
Light yellow clay -
Coloured clay
Light sand and clay
Clean sand
Gravel and sand -
Blue [Oxford] clay

Feet.
2i
3i
3
1
2
1
2
3

"IT

HUNTINGDONSHIRE.

Earith. St. Ives Extension Railway. (51 N.W.)

Communicated by Mr. A. Johnston, Resident Engineer.

• Distance from
Sutton.

4 miles 53 chains

4 „ 69 „

5 „ 20 „

5 „ 45 „

5 „ 75 „ .

Near the Old West River :

Feet

" Bear's muck " and rotten
Silt and gravel -
Gravel -
Oxford day

peat

- 15

- 3

- 12

Near engine-drain :

" Bear's muck " and rotten peat
Silt, with a few stones -
Hard gravel - - -
Oxford clay - - -

. 11
. 5
- 9

Peat and " bear's muck "
Silt and gravel -
Hard gravel

- 10
. 3

Peat and ''bear's muck"
Buttery clay
Gravel -
Oxford clay

- 8

- 4

- 13

Peat and "bear's muck "
Buttery clay
Silt and gravel -
Hard gravel

i 1 1 1

1 coooo

Digitized by VjOOQ IC

170 GEOLOGY OF THE NEIGHBOUKnOOD OF CAMBRIDGE.

APPENDIX E.

List of Works on the Geology of Cambridgeshire. Compiled
by W. Whitaker.

I. Geological Survey Publications.

Maps,

Sheet 46, N.E. (small part). By W. Whitaker and F. J. Bennett. 1869.
Sheet 52, N.E. (smaU pj^rt). By H. H. Howell. 1864.
Sheet 64 (part). By J. W. Judd. 1872.
Sheet 47 (part). By W. H. Penning. 1881.

Memoirs.

Decade XII. (Plates 9 and 10. Fish from the Kimeridge Clay, Cottenliam).

By P.ROF. T. H. Huxley. 1866.
The Geology of the London Basin. Part I. The Chalk and the Eocene Beds

of the Southern and Western Tracts (p. 45). By W. Whitaker. 1872.
The Geology of Rutland and the Parts of ... . Cambridge included in Sheet

64 of the 1-inch Map of the Geological Survey .... By J. W. Judd.

1875.
The Geology of the Fenland. By S. B. J. Skertchly. 1877-
The Geology of the N.W. part of Essex and the N.E. part of Herts, with

parts of Cambridgeshire and SuflFolk. (Explanation of Sheet 47.) 1878.
A Catalogue of the Cretaceous Fossils in the Museum of Practical Geology.

1878.

Monograph IV. The Chimaeroid Fishes of the British Cretaceous Rocks.
By E. T. Newton (pis. i., ii., vi-x., xii.). 1878.

2. Chuonological List of Books, Papers, &c.

Reprinted, with Additions and Corrections, from a List (by W. W.)
printed for the Woodwardian Museum in 1873. I have to thank
my colleague, Mr. W. H. Dalton, for his assistance in bringing this
up to date.

The many works relating merely to the drainage of the Fens have not been
included, but their titles may be found in the list in Mr. Skertchly's Memoir
on the Geology of the Fenland (see above).

Index op Authors, with the Numbers afl&xed to their Papers, &c. in the

List.

Anon., 6, 15, 58, 112.

Barrett, L., 44.

Barrois, Dr. C, 145.

Bayne, A. D., 113.

Bell, A., 114.

Bell, Prof., 60.

BedweU, C, 126.

Blake, Rev. J. F., 153, 158.

Bonney, Rev. Prof. T. G., 115, 119,

13f), 154.
Brady, H. B., 99.
Brodie, Rev. P. B., 22, 116.
Brylinski, M., 159.
Carpenter, Dr. W. B., 99.
Carter, J., 23, 127.
Craddock, T., 32.
Davidson, T., 28, 37, 94, 128.
Davies, W.,64.

Dennis, Rev. J. B. P., 52.
Duncan, Prof. P. M., 95, 96.
Fisher, M., 20.
Fisher, Rev. O., 76, 80, 105, 107, 120,

164.
Fitton, Dr. W. H., 16.
Forbes, Prof. E., 41.
Fordham, H. G., 129.
Gardner, J. S., 155, 160.
Griffith, H. F., 161.
Hailstone, Rev. Prof. J,, 3, 5.
Haime, J., 34.
Hamilton, W. J., 33.
Harmer, F. W., 108, 109.
Henslow, Rev. Prof. 24.
Hudleston, W. H., 153, 158."
Hughes, J., 138.
Jeiiyns, Rev. L., 25, 81.

Digitized by VjOOQ IC

BIBLIOGEAPHY.

171

Johnson, H. M., 130, 131, 137.
Jonas, S., 129.
Jones, Prof. T. R., 42.
Judd, Prof. J. W., 139.
Jukes-Browne, A. J., 125, 132, 140,

156, 162.
Keeping, H., 87.
Lankester, E. R., 100.
Lee, H. M., 30.
Lionnet, G,, 159.
Lunn, F., 7.
Lycett, J., 141.
M'Coy, Prof. F., 30, 31, 38.
Marshall, W., 133.
MUne-Edwards, Prof. A., 34, 88.
Mitchell, Dr, J., 17.
Moore, N., 82.
Morris, Prof. J., 28.
Okes, J., 10.
Owen, Prof. R., 18, 21, 26, 35, 45-47,

53, 63.
Penning, W. H., 146.
PhiUips, Prof. J., 101.
Porter, Dr. H., 54, 61.
Prestwich, Prof. J., 36.
Price, F. G. H., 165.
Reid, W. C, 147.
Rose, C. B., 48, 64.

Salter, J. W., 41.

Sedgwick, Rev. Prof. A., 13, 22, 27,

55 94.
Seeley, Prof. H. G., 56, 57, 59, 62,

65-67, 70-74, 77-79, 83, 89, 97, 98,

102, 103, 110, 111, 121, 134, 148-

151, 166.
Sharpe, D., 40.
Skertchly, S. B. J., 163.
Smith, W., 8, 9.

SoUas,W. J., 117, 118, 122-125, 157.
Sowerby, J., 4, 12.
Spence, — , 43.
Talbot, H. T., 142.
Teall, J. J. H., 143.
Thackeray, F., 11.
Trimmer, J., 39.
Vancouver, C, 1.
Voelcker, Dr. A., 50, 144.
Walker, J. F., 84, 85, 90-93, 104.
Walker, N., 32.
Warburton, H., 2.
Watson, W., 14.
Wells W. 51.

Wood, S. V.,iun., 75, 86, 152.
Woodward, Dr. H., 105.
Woodward, Dr. S. P., 68.
Wright, Dr., T., 49, 69, 135.

1. Vancouver, C.

2. Warburton, H.

3. Hailstone,

Prop. J.

4. Sowerby, J.

5. Hailstone,
Prof. J.

1794.

General View of the Agriculture in the County
of Cambridge. (Map of Soils. Appendix on the
Fens, with Borings.) 4to. London.

1814.

A Description of some Specimens from the neigh-
bourhood of Cambridge. ( GeoL Soc, ) Ann, of Phil.,
vol. iii. p. 72.

1815.

Rev. Supplementary Communication on Cambridge.

- (Geol. Soc) Ann. of Phil,, vol. v. p. 390. [? in-
eluded in No. 5.]

The Mineral Conchology of Great Britain, vol. i.
(p. 201). 8vo. Lond.

1816.

Rev. Outlines of the Geology of Cambridgeshire.

- Trans, Geol, Soc, vol. iii. p. 243,

6. Anon.

7. Lunn, F. -

8. Smith, W.
9.

1819.

Organic Remains (Antlers, Brink). Quart. Journ.
of Lit, Sci. and Arts, vol. vii. p. 192.

On the Strata of the Northern Division of Cam-
bridgeshire. Trans. Geol. Soc, vol. v., p. l\4.

Geological View and Section of the Country be-
tween London and Cambridge.

Geological View and Section through Suffolk to
Ely.

Digitized by VjOOQ IC

172 GEOLOGY OF THE NEIGHBOURHOOD OF OAMBEIDGE.

10. Okbs, J. -

11. Thackeray^ F.

12. SOWERBY, J.

13. Sedgwick, Rev.
Prof. A.

14. Watson, W.

15. Anon.

16. FiTTON, Dr. W. H.

17. Mitchell, Dr. J. •

18. Owen, [Prof.] R. -

19. Owen, Prof. R.

20. Fisher, M. -

21. Owen, Prof. R.

22. Brodie, Rev. P. B.

1821.

An Account of some Fossil remains of the
Beaver, found in Cambridgeshire. Trans. Camb,
PAt/. 5oc., vol. i. p. 175.

1822.

On a remarkable instance of Foissil Organic Re-
mains found near Streatham* in the Isle o£ Bly.
Trans, Camb. Phil, Soc., vol. i. part ii. p. 469.

1824, 1825.

The Mineral Conchology of Great Britain, vol. v.
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The Rock of the Cambridge Greensaiid. G^o2.
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1867.

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1868.

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1873.

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139. JUDD, J. W.

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490,

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153. Blake, Rev. J. F., On the Corallian Rocks of England^ Quart,

AND W. H. Hud- Jfyum, Geol. Soc, vol. zxxiii. p. 260, (Gambridge-
LE8T0N. shire, pp. 313-316, 398.)

154. BoNNEYy Rev. T. G. [Gorallian of Upward.] GeoL Mag., dec. ii.

vol. iv., October.

155. Gardner, J. S. - On British Cretaceous Patellidse and other

Families of Patelloid Gasteropoda. Quarh Joum.
GeoL Soc, vol. xxziii. p. 192« (Cambridge, pp.
201, 202.)

156. Jukes-Browne, A. J. Supplementary Notes on the Fauna of the

Cambridge Greensand. Qmrt. Joum, GeoL Soc,
vol. xxxiii. p. 485.
157* SoLLAS, W. J. » On Pharetrospongia Strahani, SoUas, a fossil
Holoraphidote Sponge from the Cambridge " Co-
prolite '' Bed# Ciiart. Joum, Geol. Soc, vol. zxxiii.
p. 242.

1878.

158. Blake,Rev.J.F., and The Coral Rag of Upware. GeoL Mag., dec. ii.

W.H. HuDLESTON. vol. V. p. 90.

159. Brylinski, M., and Phosphates de Chaux fossiles Geologic et

G. LiONNET. Ori^ine, Applications au Agriculture. BuU, Soc

GM, Norm., t. iv., p. 3; Phosphorites du Cam'
bridge, pp. 92-97.

160. Gardner, J. S. - On the Cretaceous Dentaliidae. Quart, Joum.

Geol Soc, vol. xxxiv. p. 56.

161. Grif'fith, a. F, - On a Flint Implement fr6m the Barnwell

Gravel. Geol, Mag., dec. ii. vol. v. p. 400.

162. Jukes-Browne,A. J. The Post-Tertiary Deposits of Cambridgeshire.

8vo. Cambridge and London.

163. Skertchly, S. B. J. The Geological part of "The Fenland Past and

Present" (by Miller and Skertchly). 870. Wis-
bech and London.

1879.

164. Fisher, Rev, O. - On a Mammaliferous Deposit at Barrington,

near Cambridge. Quart, Joum, GeoL Soc, vol,
XXXV. p. 670.

165. Price, F. G. H. • The Gault, being the substance of a Lecture

delivered in the Woodwardian Museum, Cam-
bridge. 8vo. London.

166. Sbsley, Prof. H. G. On the Dinosauria of the Cambridge Greensand.

Quart, Joum, Geol, Soc, vol. xxxv. p. 591.

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181

INDEX.

Abington Grange, Chalk-pit near, 63.

Park, Boulder Clay near, 74 ;

Chalk Rock near, 67.
Agriculture, 127.
Allen, H. A., 132,134.
Alluvium, 112, 128.
Analysis of rocks, etc., 26, 43, 55, 66.
Arbury, gravel at, 99.
Ashdon, „ 73, 79.

Ashwell, Tottemhoe Stone at, 42.

Babraham, Boulder Clay at, 74, 76 ;

chalk at, 61, 63 ; urells at, 155.
Bacon, Dr., 160.
Balsham, Chalk-pits at, 71 ; gravel

and loam near, 85, 87 : weUs at,

155.
Barnwell, Gault at, 18; gravels, 97,

124; well at, 155.
Barrols, Dr. C, 20, 55, 60, 134-136,

138, 139.
Barrington, Boulder Clay at, 75 ; Cam-
bridge Greensand at, 35 ; gravel near,

94 ; Grey Chalk at, 53 ; wells at,

155.
Barriii^n Hill, 74, 76, 79.
Barton, Cambridge Greensand at, 38 ;

gravel at, 96 ; well at, 156.
Bartlow, Boulder Clay at, 75 ; gravel

at, 85.
Bell, A., 106.
Bluntisham, Boulder Clay at, 75 ;

borings at, 167, 168 ; gravels near,

81, 110, 111 ; Oxford Clay at, 5.
Bonney, Prof. T. G., 6, 20, 26.
Bottisham Load, Cambridge Greensand

at, 134; Gault at, 19, 134 ; wells at,

156.
Boulder Clay, 73, 119; denudation of,

124 ; formation of, 115 ; local rocks

in, 119 ; soil of, 228.
Bourn, Boulder Clay near, 75 ; Lower

Greensand at, 11, 75 ; well at, 156.
Bourn Brook and Valley, 105 , 123.
Boxworth, Kimeridge Clay at, 4, 7.
Brassel, 41, 48.
Brodie, Kev. P. B., 98.
Brooklands Parm, gravel at, 97.
Brown, Dr. R., 118.
Bnrwell, Chalk Marl at, 41 ; Tottem-
hoe Stone at, 46.
Caldecote, well at, 157.
Cam Valley, gravels of, 94 j physical

history of, 123.

Cambridge, Chalk Marl at, 32, 102;
depth of wells at, 15 ; Gault at, 17 ;
gravels at, 89, 97, 101-103, 105 ;
situation of, 1 ; wells at, 157, 158.

Cambridge Greensand, 24 ; Fossils of,
29, 132 ; Gault fossils in, 29, 145.

Carleton Grange, Chalk near, 68;
gravel at, 87.

Carver, F. J., 163, 166.

Caxton End, Lower Greensand at, 11.

Cenomanian, 20, 138.

Chalk, classification of, 20, 21 ; eco-
nomics of, 127 ; Flexures of, 67,
115 ; Water-supply of, 129.

Chalk Marl, 23, 39; Fossils «f, 42,
133.

Chalk Rock, 22, 66 ; analysis of, 66 ;
fossils of, 69, 136.

Chatteris, storms at, 3.

Cherry Hinton, Chalk Mail at, 40, 44,
50 ; Melboum Rock at, 55 ; Tottern-
ho8 Stone at, 44 ; Zone of Holaster
subglobosus at, 50; wells at, 159.

Chesterford, Loam at, 71.

Chesterton, Borings at, 159, 168 ; Cam-
bridge Greensand at, 38 ; gravels at,
99, 103, 105.

Chloritic Marl, 24.

Clayhithe, Cambridge Greensand at,
33 ; Gault at, 19.

Coast-ice, action of, 117.

Coe, — , 157, 158.

Coldham Common, 15, 32, 157.

Colne, gravel at, 110.

Comberton, gravel at, 96.

Coning^on, well at, 159.

Coprolite bed, 24.

Coprolites, excavation of, 126 ; nature
of, 26 ; origin of, 27.

Coton, Cambridge Greensand at, 35 ;
well at, 159.

Cottenham, Gault at, 12, 19; Lower
Greensand at, 11, 12 ; well at, 160.

Coulson, — , 157.

Croft Town, gravel at, 103.

Davey, E. C, 22.

Denny Abbey, gravels near, 100, 104.

Dry Drayton, well at, 1 60.

Dallingham, gravel near, 91, 93 ; chalk-
quarry near, 65; railway • cutting
near, 75, 93.

Dungate Farm, gravel at, 86.

Duxford Grange, gravel at, 84.

Digitized by VjOOQ IC

182

INDEX.

Earith Wash, borings in, 169.

Slsirorth Bock, 6, 7.

JSvans, Dr. J., 1 12.

Evans, C. 138.

Eyersden, BriclLyard at, 17; Boulder

Clay near, 75; Lower Chalk at,

53; well at, 160.
Eming, gravel near, 92.

Fen Ditton, Cambridge Greensand at,

32, 112; wells at, 160.
Fenny Stanton, gravel -at, 110.
Fens, The, 113, 128.
Fisher, Bev. O., 35, 94, 99, 113.
Fitton, Dr., 24.
Flavel, — , 156-163, 165-167.
Fleam Dyke, coarse of, 109.
Flint Implements in the Fens, 112.
Flints in Middle Chalk, 61, 64; in

Upper Chalk, 70.
Flood Gravels, 121.
Forbes, Prof. E., 140.
Fordham, H. G., 167.
Foolmire, Melboum Bock near, 57.
Foxton, Gravels at, 94 ; Melboorn

Bock at, 57 ; Zone of Holaster sub-

globoBUS at, 52.
Fulbonm, Totternhoe Stone, at, 44;

wells at, 160; Zone of Holaster

subglobosos at, 52.
Fnlboum Fen, 108, 112.

Gault, 13 ; erosion of, 16, 38 ; econo-
mics of, 126.

Girton, gravel at, 90 ; well at, 161.

Gog Magog Hills, Chalk of, 61, 62 ;
gravels on, 80; water-level below,
130.

Grantchester, Alluvium near, 112 ;
Cambridge Greensand at ; 37, 39 ;
Grault at, 17 ; Gravels at ; 96, 105.

Gravels, Fossils of, 106 ; Glacial, 73,
79 ; of ancient river system, 82 ; of
present river system, 94 ; water-
supply of; 131.

Grey Chalk, 21, 43.

Griffith, A. F., 98.

Gruner, M. L., 28.

Guilden Morden, well at, 167.

Hadstock, Glacial gravel at, 73;
Spring, at, 131.

Hailstone, Prof., 24, 44, 46, 48.

Hardwick, Boulder Clay at, 23, 75 ;
well at, 161.

Harlton, Cambridge Greensand at, 31 ;
Chalk Marl at, 41 ; Totternhoe
Stone at, 44; Warp at, 114; well
at, 161.

Harston, Cambridge Greensand at,
31, 35; Melbourn Bock at, 56;
rainwash at, 114 ; Totternhoe
Stone at, 44.

Haslingfield, Cambridge Greensand at,
36, 37 ; Gault at, 17, 19 ; Tottern-
hoe Stone at, 47; Warp at, 114;
wells at, 161.

Hatley St. George, well at, 162.

Hauxton, gravel near, 105.
Hauxton Bridge, pits near, 31, 40.
Hubert, Prof., 20, 134.
Heydon, Chalk Bock, at, 67.
Hildersham, Boulder Clay at, 79 ;

jgravel at, 104.
Hmde,Pro£: Y., 118.
Hinton, Cottage, 96.
Histon, gravels at, 90, 99, 100 ; well

at, 162.
Holywell, gravel, at, 110; spring at,

131.
Homingsey, coprolite-pits at, 33, 39 ;

Gault at, 19; gravel at, 105, 112;

well at, 162.

Ice-floes, action of, 117.
Ickleton, chalk-pits near, 64.
Impington, Grault at, 18; gravel at,

99, 100.
Ingold, J., 163, 164.
Isaacson, — ,165.

Jenyns, Bev. L., 113, 127, 128.
Johnson, N. W., 155, 166, 159-161.
Johnston, A., 169.

Eimeridge Clay, 9; economics of^

128 I fossils of, 10.
Kingston, Chalk Marl at, 41 ; well at*

162.
Knapwell, Eimeridge, Clay at, 4, 9.
Eneesworth, Totterahoe Stone at, 43,

41.

Landbeach, Gault at, 19 ; gravels near,

110,113.
Larks Hall, gravel near, 87.
Lee, — , 155, 158.
Linton, Boulder Clay, at, 75 ; Chalk at,

64.
Litlington, Melboum Bock at, 58.
Little Trees Hill, chalk-pit at, 61.
Lolworth, Gault at, 18 ; well at, 162.
Long Stanton, Boulder Clay near, 75 ;

gravel ridge near, 90.
Lower Chalk, 43, 137 ; Fauna of, 138.
Lower Greensand, 11; water-supply

of, 129.

Madingley, Chalk Marl at, 23, 41 ;

wells at ; 162.
Melbourn, Quarries at, 57.
Melboum Bock, 22, 55 ; analysis of,

55 ; fossils 0^ 60, 134.
Meldreth, wells at, 163.
Middle Chalk, 55, 137 ; fauna o( 139.
Middle Glacial, absence of, 115.
Milne, Prof. J., 117.
Milton, gravel at, 103, 105.
Missleton Hill, Chalk of, 63.
Mutlow Hill, Chalk of, 64.

Needingworth, gravel at, 110.
Newmarket, gravels near, 91, 92, 111.
Newsells Bury, Chalk at, 75.
Newton, Chalk at, 52.

Digitized by VjOOQ IC

INDEX.

ia3

Newton, E. T., 149.

North Hall, gravel-pits mear, 83.

Oakington, grayels at, 90 ; Lower
Greensand at, 11.

Orwell, Boulder Clay at, 75 ; Cam-
bridge Greensand at, 35 ; Grey Chalk
at, 53 ; Tottemhoe Stone at, 53 ;
well at, 163.

Case, valley of the, 6, 109.

Over, Boulder Clay near, 75 ; gravel
at, 91, 111.

Oxford Clay, 5f economics of, 126;
fossils o^ 7.

Fampisford, gravel near, 95 ; well at,

163.
Peat, 8, 112.

Phosphate nodules, 26, 48, 127.
Pidley, gravel near, 81.
Pidley Fen, 3.
Piggott, B., 162, 166.
Pluvial period, 121.
Pond, — , 161.
Post Glacial Drifts, 82, 120.
Prestwich, Prof., 121.
Price, P. G. H., 21, 134, 137, 138.

Qny-cum-Stow, 40, 88, 108.

Kiun&ll, disposal of, in ewrly Post-
glaciaJ times, 122 ; absorption of, in
later times, 124.

Rampton, borings at, 168.

Ramsay, Prof., 115, 120.

Beach, Chalk Marl at, 41 ; nodule-bed
in Ganlt at, 34 ; Tottemhoe Stone at,
48.

Bedland Hill, 57, 85.

Rhee valley, history of; 94, 125.

Bock-beds in chalk, 22; in Oxford
Clay, 6, 7.

Royston, Boulder Clay near, 75 ; Mel-
bourn Rock near, 58 ; Middle Chalk
at, 63.

Rutley, P., 24.

St Ives, Boulder Clay near, 75 ; brick-
yards at, 6 ; gravel at. 111.

St. Ives Bock, 6.

Sandy, Lower Greensand at, 12.

Sawstou, well at, 164.

Sedgwick, Prof., 17, 24, 80, 82.

Seeley, Prof., 6, 20, 25, 89, 90, 98, 156,
159.

Senonian, 20.

Shardelow's Well, 45, 108.

Sharpens, gravel at, 83.

Shelford, gravels at, 95, 101 ; Grey
Chalk at, 51, 56 ; MelbournKock at,
56 ; wells at, 164.

Shepreth, Tottemhoe Stone at, 44.

Signal Hill, gravel at, 80.

Six-Mile-Bottom, gravel at, 87.

Skertchly, S. B. J., 120, 121.

Smyth's End, chalk-pit at, 67, 75.

Sollas, W. J., 17.

Somersham, gravels near, 110; spring

at, 131.
Springs, alteration in position of, 124 ;

near graveyards, 131.
Stanmoor Hall, Chalk and gravel at,

61.
Stapleford, gravel at, 101 ; well at,

164.
Stetchworth, Chalk Rock at, 68.
Storms near Chatteris, 3.
Streatham Fen, wells in, 115.
Swaffham Abbey, Chalk Marl near,

41.
Swaffham Bulbeck, Melbourn Bock at,

59 ; wells at, 165 ; Zone of Holaster

subglobosus at, 52.
Swaffham Fen, Cambridge Greensand

in, 34 ; Gault in, 34; peat and sand

in, 112.
Swaffham Prior, Tottemhoe Stone at,

45 ; wells at, 165 ; Zone of Holaster

subglobosus at, 53.

Tebbuts,— , 167.

Tharfield, loam near, 81.

Thoday, — , 165.

Tomlison, H., 129, 155, 159, 160, 162,

164, 166.
Topley, W., 13.
Tottemhoe Stone, 22, 43 ; analysis of,

43 ; fossils of, 49, 133 ; water-supply

from, 130.
Trail, 35, 36, 113.
Triminer, Joshua, 113.
Trumpington, Cambridge Greensand at,

31 ; gravels near, 95 ; wells at, 165.
Turonian, 20, 138.
Tylor, A., 121.

Upper Chalk, 69.

Upper GrecDsand, absence of, 24.

Valleys, relative ages of, 123.
Vandlebury, Chalk of, 22, 63 ; well at,

166.
Voelcker, Dr., 26.

Wadley Hall, gravel near, 87, 109.
Wardington Bottom, 67, 83, 115.
Warp, 36, 114.
Waterbeach, gravel at, 103, 105 ; wells

at, 166.
Water-supply, 128.
Wendy, Chalk Marl near, 35 ; well at,

166.
Westley Bottom, 109.
Westley Lodge, chalk-pit near, 65.
Westley Waterless, Chalk Rock near,

68 ; loam near, 80.
Westwick, Lower Greensand at, 11.
West Wickham, Chalk near, 71.
Whaddon, Cambridge Greensand at,

31,85; wells at, 166.
Whitaker, W., 20-22, 43, 50, 58, 66,

79, 98, 170.
Whitwell Farm, Cambridge Greensand

at, 38.

Digitized by VjOOQ IC

184

INDEX.

Whittlesford, gravel-pits near, 84, 104.

Wickcn, well at, 167.

Wilbraham, Chalk near, 61 ; gravels
near, 86, 88.

Wilbraham Fen and River, 108.

Williugham, boring near, 168 ; gravel
near, 91.

Wimpole, Cambridge Greensand at,
36 ; wells at, 166.

Worsted Lodge, gravel near, 80 ; Mid-
dle Chalk at, 64.

Wratting Valley Farm, gravel near,
86.

Zone of Ammonites interruptns, 17,

19.
Zone of Holastcr subglobosus, 50, 134.
Zone of Micraster corbovis, 69, 136.
Zone of Ehynchonella Cuvieri, 60,

135.
Zone of Ehynchonella MartiDi, 39.
Zone of Terebratulina gracilis, 62, 135.

LONDON:

Printt^d by George E. Etre and William Spottibwoodu,

Printers to the Queen's most Excellent Majesty.

For Her Majesty's Stationery Office.

[6003.— 5O0.—0/81.]

Digitized by VjQOQ IC

rlu,i>. I

GEOLOGICAL SURVEY of ENGLAND and WALES.

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GEOLOGICAL SURVEY of ENGLAND and WALES.

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